BGAS-1

Painting Inspector ZCorr Level I

Ruane - TAT1 TRAINING & WM~NATIONS IN INSPECTION &

NON -DESTRUC1-IVE TESTING

1 A, Persiaran Melor, Bandar Pelancongan Pant$ Kijal, 241 00 Kijal, Terengganu, ~alaysia. Tel: 609-864 1044 Fax: 609-864 1043 Ernail: [email protected] /

T A B L E O F C O N T E N T S

CORROSION .......................................................................... SURFACE PREPARATION ............................................................

Dry abrasive blasting ..................................................................... Wet blasting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Hand and power tool cleaning ............................................................. Flame cleaning ........................................................................... Chemical cleaning ........................................................................

SURFACE PREPARATION (NON-FERROUS) .......................................... TESTS T O DETECT SURFACE CONTAMINATION ................................... PAINT CONSTITUENTS ...............................................................

Binder .................................................................................... Pigments ................................................................................. Solvents .................................................................................. Other constituents ........................................................................ Solutions and dispersions .................................................................

PAINT DRYING AND CURING ........................................................ COATING$YSTEMS ...................................................................

Corrosion protection methods .............................................................

Layers of a paint film .....................................................................

Types of coating system ..................................................................

PAINT TESTING - GENERAL ......................................................... FLASHPOINT .......................................................................... VISCOSITY ............................................................................ DENSITY ............................................................................... WET FILM THICKNESS (WFT) . ... .................................................... DRY FILM THICKNESS (DFT) .........................................................

Non-destructive test gauges ................................................................

Destructive test gauges .................................................................... Test pancls ................................................................................ Calculation ................................................................................

ADHESION ............................................................................. Vcc cut lest ...............................................................................

Cross-cut test (cross hatch test) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

X-cut lapc test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1)olly lest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1-1 ytll.aulic ;~clhesion test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

HOI. 1I)AY DETECTION ................................................................ I4igh volt;~gc holiday detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Wcl spongc pinhole detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SAkII'LING

............................................................. WEATHER CONDITIONS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Relative humidity (RH%) and dew poinl

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Metal temperature

................................................................. PAINT APPLICATION

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Brush application

......................................................................... Roller application

......................................................................... Spray application

............................................... APPLICATION O F METAL COATINGS

.................................................................... C O A n N G FAULTS

................................................................... HEALTH & SAFETY

................................................................ COSHH Regulations 1994

.................................................... Occupational Exposure Limits (EH40)

.............................................................. Volatile organic compounds

................................................................. Health & Safety data sheet

.......................................................................... INSPECTION

.............................................................. Duties of a painting inspector

....................................................................... Reports and records

........................................ Knowledge required to perform painting inspection

............................................................ Typical contractor malpractices

PAINTDATASHEETS ................................................................. ............................................................... QUALITY ASSURANCE

.......................................................... NORMATIVE DOCUMENTS

Corrosion is generally an electro-chemical process which results from an anodic

reaction and at least one ca~hod ic reaction. The corrosion of steel takes placc at the 1 anode.

An elecrrolyre i.r u medium which will allow the pmsuge of elecrricul current consisring of u chernicul sulr di.rsolved in wurer.

The greater the amunr of chernicul sulr present. the berrer rlze conducriviry of the elecrrolyre.

( The anodic reaction is expressed as lollows:

( For iron and steel this would be expressed as:

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Fe -+ Fe* + 2e-

At least one of Five basic reactions may take place at the cathode. The most common reaction applicable to the corrosion of steel is as follows:

M + M+"+ne

Where: M = element involved n = a number c = electron(s)

Iron ore is an oxide of iron in chemical balance with the environment; when this iron ore is converted to iron, the chemical balance is changed and the iron becomes active,

i.e. it corrodes on contact with the natural environment and tries 00 revert back to its natural inert state. The natural environment usually contains moisture (which provides the electrolyte) giving the following simultaneous reactions:

The products of these reactions take part in further reactions with the immediate

I Corrosion reactions can be accelerated by the existence of certain cri~eria including:

4 0

( I . variati0.n~ in oxygen content on the material's surface:

environment leading to the formation of corrosion products, the most familiar being rust.

Mill scule of I 2. the concentration of chemical sale in the clectrolyte. e . g chlorides and sulphates; irott produced when rlte zreel is n~unufucrured; ir ix u rexulr ofrlte hor sreel coming inro conrcrcr wirh uir und forming an oxide composed rr / rhree 1uyer.r: FeO necrresr the sreel. Fe,,O, then Fe,O, on rlre ourside. Mi l l scule h a u roral thickness berween upproximurely 25 pm und 100 pm.

3. other metals or metal compounds of higher nob i l i v (more electro-positive) in contact with the steel. e.g. mill scale;

4. acids or alkalis;

5. certain types of bacteria near the material's surface.

6. high temperature. The higher the temperature the greatcr the rate of corrosion.

The following list shows some rnetalsJmeta1 compounds in their order of nobility in sea water at ambient temperature. Thc relative positions of the metalsJrneta1 compounds in the list can change with a change in electrolyte typc or temperature; this list is known as the galvanic series.

'01 Gold NOBLE Silver

Nickel

Copper

Mill scalc

Mild steel

I Alu~niniu~n Zinc

Magnesium IGNOBLE

Excrrnple: I f steel was in intirl~ate contact with zinc or attachcd to zinc via a wire in an elcctrolyte, e.g. soil or water. the zinc would corrode first because steel is more nohlc than zinc. In this cxaniple the zinc bcconics the anode and the steel the cathode, i.e. thc srecl is being cn~hotlicnlly/~ro~ectocI and the zinc is acling 2s a sncrificic~l atrode.

Ruane & T P OINei/

I Stmd 1.1 rror d11tl~erorr.r ur11e.r.r 11 1.1 I ~ I ~ I ~ T I fitrr11 when tr C~III b~ lr~htrlert, e.,v. rflcr frtr,$*rnerlrtrrr(,n dir rin,p d r v bltr.rrrn~ rywrtrrlr,rl.r

Correct surfacc preparation is a vitally important stage for most coating systems, i t is often thc process which governs the service life of thc coating system.

There are various ways to prcparc a surface prior to coating:

Abrasive blast cleaning Wire brushing Scraping Grinding Needlc gunning Chemical cleaning Water blasting Weathering Flame cleaning Vapour degreasing

Dry abrasive blasting

m

The quulity of a surface preparation is governed by the amount of surface contaminant remaining on the substrate after cleaning. although i t may also relate to the resultant surface texture, e.g. the surface profile on a substrate after abrasive b~last cleaning.

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Both rnetallic and mincral abrasives are commonly used for blasting, for example:

Steel or chilled iron grit Steel sllot Metallic grit and shot mixed Copperslag Garnet Sand

Dry abrasive blasting is carried out by projecting a highly concentrated stream of small abrasive particles onto the substrates surface at speeds up to approximately 720 k m h (450 m.p.h.). The operation removes rust. scale, dirt and any other extraneous material from the substrate and also leaves an irregular profile which provides an ideal key for coating adhesion. Dry abrasive blasting is often the best method of surface preparation for long term protection coating systems.

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The Cun[rol of Su1~src1nce.s 1fuzarclou.s ro Iiccrlrl~ Kegulations 1994 (CCISHH Regula[ions) do not allow the usc of' sand containing free silica in dry blasting operations bccausc of' the associated hcalth Ila7.ard of silicosis.

There are otl~cr ohrasivcs which are used, usu:~lly for specialised applications. e.g. walnut shells. ceramic grits, crushed glass, aluminium silicate.

Abrasives The degree of surfacc roughness and rate of cleaning is partially governed by the characteristics of the abrasive used; these being:

Size Hardness Density Shapc

Effect of abrasives

Grit is angular in profile with sharp cutting edges: i t shatters mill scale and untlcrcuts any surlhce co~~tnlninant resulting i n n clean surl'ace with a rough profile. Tllc amplitude tends to he quite erratic with a lurgc occurrence of rogue pecrks, cspccially when blasting i n one iirca I'or too long.

Ruane & T P OeNei/

.. . stand our ubovc rhe required prc,lile and should be avoided if upplying rhirr coririrtgs us rhey may lead ro spot orflush rusring.

Rogue p e o ~ n r e p e u ~ which

Blusr finishes produced in produ~.lion should nor be

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rouched with bare hunds due ro conraminorion.

S l ~ o t is spherical. i t shatters mill scale, but does not have sharp cutting edges t a surface, liowcver, the visual appearance of a shot blasted finish is sirnilar blasted finish although there is less roughness to the touch. Shot blasting worl a steel surface to a greater degree than grit, which has the effect of reducing th or any stress corrosion cracking which could otherwise occur in the ruture. : reduces the occurrence of rogue peaks but may press impurities into the surface

All (lccurule I I I C U . T I I I ~ ~ I I ~

equipmcnr, e . ~ . dial micromerers. should be issued with r~ulibruriort ~erl if i~.ures or certr/icrilc.r of cor l /~nnnn~'c ro five urrruruncc rhclr rite rectdings ol~ttiined ore goirtg Irl Ilt correct wirhin u rkrtcd murgin of crrmr.

It is common practice to mix metallic shot and grit to obtain a blast finish clo: ideal (a typical mix being 70-80% shot and 20-30% grit).

Surface profile The shape of a cross-seclioned blast finish is known as the surface profile or pattern.

Amplitude Rogue peaks Peak Trough ,

I SURFACE PROFILE

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SURFACE PROFILE GAUGE

The size of the profile as measured from the peaks to the troughs is known as nnlpliirrcie or peak t o trough heigltt, and is primarily governed by the size of a b r ~ used, although other [actors are important, e.g. angle of impingement, hardness surface and other characteristics of thc abrasive itself. Maximum amplitudes amplitude ranges would normally be quoted in specifications, a typical amplitude rai for liquid paints would be in the region 01 30-75 pm.

The amplitude of a blasted surFace may be measured by a nurnber of rnetho including the use o f a surface profile needle garye. surfnce repliccc rape. e.g. Tes [ape, or a surface compamror.

'O

Surface profile needle gauge

This relies on a needle reachlng the bottom of the troughs on the surface profi Because there are so rnany troughs of different depth. it 1s normal, and necessary, lakc tcn or twenty rcadings and calculate the avcragc ampl~tudc. Bcfore taking a readings ~t is necessary to zero the gauge on a flat piece of glass

Ruane & // T P O'Nei

Surface replica tape

It is rmporfant to nnre thut tleedle gauges. sudace replicu tupe and surface comparators only gives the degree of roufhness

Testex /ape is a tradc narnc of a commonly uscd or surfacc rcplica tapc. It is uscd In conjunction with a dial micrometer and although quite costly, has thc advantage ol' providing a permanent record. 'The procedure for carrying out this test is as follows:

101 1. Zero the micrometer ensuring the flat contact points are clean.

I 2. Remove paper backing and stick Tester tape to the surface to be measured

3. Rub the Testex paste into the troughs using a blunt instrument, until the peaks can be seen butting up to the transparent plastic.

4 . Remove the Testex tape from the surface and measure the overall thickness with the dial micrometer.

5 . Deduct 50 pm (2 thou") from the reading to obtain the amplitude. The plastic (mylar) film to which the soft compound is attached is 50 pm thick.

I Surface comparator

A profile grading can be given when the area under assessment is rougher than the smoothest of two adjacent areas on the comparator but not as rough as the rougher of the two areas. The profile is then graded according to the following:

Fine profile: Equal to or rougher than area 1 but not as rough as area 2. Medium profile: Equal to or rougher than area 2 but not as rough as area 3. Coarse profile: Equal to or rougher than urea 3 but not as rough as nrea 4.

30 The roughness of the surface to be assessed is compared to the different areas on thc comparator by visual examination and i f necessary by scraping with a finger nail, small wooden stick or similar - never with the fleshy part of the finger as this will contaminate the blast.

Blasting grades The gmrle of a blasr finish relates to the amount of' surface contaminant rcmalning after blast~ng. Thc grade of blast finish is primarily governed by blasting time and thc velocity of the abrasive particles.

ctnd not the deXre> of clectt~li~~e.ts.

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BS 7079 : Part A 1

BS 7079 - PI-eprrrrrtion of steel substrates Def~re application of pairits atld relater1 prod~rcts. Part A l ol' this standard is pictorial and shows rust grades prior to blasting and the degrec of surface cleanliness aI'ter blasting.

I f the profile is finer than area 1 it is termed finer than fine.

If the profile IS coarser than area 4 i t is termed coarser than coarse.

BS 7079 : Purt A I is fhe surr~e c1.t IS0 RSOI -I and SS 05 59 00.

I Rust grades:

70

I A - Stcel surfacc largely covered with atlhcrent mill scale but little, i f any, rust

TIC surface undcr examination is visually conlpared with high quality photographs In thc standard both before and after blasting. The preparation is then given a coding, e.g. C Sn2% which can be interpreted using the following extract from the standard:

II - Stccl surfacc which has begun to rust and from which thc mill scnlc has hcg~ln to Hake.

C - Stccl surracc on whicll ~ h c ~nill sc;lle has rustcd away or fro111 which i r can I)c scraped. ~ L I I with slight pittirlg visible undcr nonnal vision.

D - Stccl surf'acc on which the mill scale has rusted away and on wh~ch gcncral pitting is visible under normal vision.

Prcp; l ra t io~~ gradcs - blast cleaning.

f'ric~r lo hlasl clcaning, any heavy layers of' rust shall be rcniovctl I1y chipping. Vl>ihlc 0 1 1 , grcasc and dirt shall also I7c rcrliovccl.

Alrcr hl ; lhl clcaning, the surf'Acc shall hc clc;~nccl f'rorli loosc dust ancl debris.

S a l - Light blast cleaning. When viewed without magnification, the surfac shall be free from visible oil, grease and dirt, and from poorly adhering mil scale, rust, paint coatings and foreign matter.

Sa2 - Thorough blast cleaning. When viewed without magnification, tht surface shall be free from visible oil. grease and dirt, and from most of the mill scale, rust, paint coatings and foreign matter. Any residual contamination shall be firmly adhering.

Sa2'/2 - Very thorough blast cleaning. When viewed without magnification, the surface shall be free from visible oil, grease and dirt, and from mill scale. rust, paint coatings and foreign matter. Any remaining traces o f contamination shall show only as slight stains in the form of spots or stripes.

Sa3 - Blast cleaning to visually clean steel. When viewed without magnification, the surface shall be free from visible oil, grease and dirt, and shall be free from mill scale, rust, paint coatings and foreign matter. It shall have a uniform metallic colour.

Equipment

Centrifugal blast units

Blasting in factories is often carried out using rotating wheels which throw the abrasive at the component. These units, known as centriflrgal blast wheels, are usually fixed installations and are commonly used for large production runs, e.g. on pipes in pipe inills and large steel plates in shipyards.

COMPARISON O F BLASTING GRADES

The main advantages of this system compared to air blasting systems are as follows:

SSPC

- White metal (SP5)

Near white metal (SPIO)

Commercial finish (SP6)

Light blast and brush off (SP7)

a. lower cleaning time. b. lower abrasive consumption. c. lower energy consumption, d. less labour used. e. more consistent and uniform blast finislics. I: more environment liiendly,

g. safer to implement - closccl .r)~.r/cnz.

The abrasive is fed into the centre of the whccls and to the inner edges of the attached bla(1cs by means of an impeller. The abrasive is then accelerated to the end of the blaclcs and onto thc component by ccntl.il'ugal lol-ce at spccds typically between 250-350 k~nlh (I 60-220 m.p.11.).

SSPC = Steel Structures Painting Council NACE = National Association of Corrosion Engineers

BS 7079 (SS 05 59 00)

Sa3

Sa2%

Sa2

Sa 1

For cos! reasons the abrasive used w o ~ ~ l d norrctully he reusable. The abrasive is rccyclcd LIP to approximately twenty timcs provicliclg i t is l'rcc from grcase or 011

co~ltamination. An air-n)c~.ih s~parator relnovcs any dust contarninanls from recycled ;thras~vc bclorc i t is led back into the wllcels.

NACE

Grade I

Grade 2

Grade 3

Grade 4

Ruane & P oweill

/ Air blasting

Pressure Olusring, which is a type of air blasting systcrn, would normally be used on

site work. Vacurtm Olasr and sucfiott blusr equipment also come under the category of air blasting but are not as widely used due to lower efficiency.

,,

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( Blasting nozzles

Pressure blasting equipn~enl basically consists of:

a compressor, providing an air supply of approximately 0.7 MPa ( I00 p.s.i.), a pressurised pol containing the abrasive. liquid separators, i.e. moisture fillen (knock-our pots),

a carbon impregnated hose, a Venluri shaped blasting nozzle, a dead mans handle for direct operator control.

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40

Blasting nozzles are available in a variety of materials and orifice sizes. Sometimes the nozzles are lined with relatively abrasive resistant materials. c.g. tungsten carbide. for n longer working life.

The velocity of abrasive particles leaving a blasting nozzle is primarily governed by the pressure at the nozzle; the higher the pressure the higher the velocity and therefore the higher the rate of cleaning.

There is a point at which an increase in pressure does not increase the velocity substantially, this is at approximately 0.7 MPa (100 p.s.i.) depending on the abrasive used. Limiting pressures to 0.7 MPa (100 p.s.i.) is also advantageous for safety reasons.

It is important to keep the pressure at the nozzle as close to 0.7 MPa ( I00 p.s.i.) as possible because for every I% loss in pressure there is approximately a I%% loss in efficiency. The pressure at the nozzle may be measured using a hypodermic needle gauge, this is placed through the hose near the nozzle. with the hole in the needle facing the nozzle.

I Two types of nozzle which exist are the srl-flight bore nozzle and thc Verlruri strrrpecl nozzle. Straight bore nozzles are rarely used for blasting large surface areas because hey are not as efficient as Venturi shaped nozzles. The velocity of abrasive leaving a straight bore nozzlc at 0.7 MPa (100 p.s.i.) is approximarely 350 k m h (220 m.p.h.). whereas the velocity for a Venturi shaped nozzle under similar conditions would be approximately 720 km/h (450 m.p.h.).

Slreiohl Bore Nozzle.

I Venlud Shaped Nozzle.

Safcty

Ccrltril'ugal blast units arc it close(/ sys[cn~, 1.e I I U I I I ; I I ~ ;~cccss to the hlasling arcn I S

I~mircd. When ilslriy ;In o p ~ r ~ syste~n, e.g. for site t)l;lstirlg ;~pplications using prcssurc

00

Venturi sh;~ped nozzlcs illso produce a larger hlast pattern with the whole area rccciving a relatively equal amount oS abrasive, wlicreas, a s~raight bore nozzlc concentrates most of thc abrasive in the ccnlral arca of the blast pattern. resulting in a Sringc arca of Iowcr I,lasLic~~ efficiency.

Ruane & T P o m B

blasting equipment, access is not usually restricted, therefore warning sign: necessary and rcgular inspection of the equipment is rcquircd.

1 Other safety considerations relating to pressure blasting are i s lollows:

Use of carbon impregnated hose to reduce the chance of static shock. Use of a dead-mans handle to stop the flow of abrasive when the operator le of the nozzle. Keeping hoses as straight as possible to prevent kinks which may lead blow-out. Use of hoses of the correct type, i.e. reinforced. Use of external couplings if joining hoses together. Internal couplings reducc bore and the eroding action of the abrasive could lead to a blow-out. Restricting the pressure to 0.7 MPa (100 p.s.i.). The wearing of protective clothing. including an air fed helmet, boots, lea apron and gloves.

Wet blasting Wet blasting methods are good for removing soluble salts such as chlorides fr surfaces and are good for the removal of toxic coatings, e.g. red lead paint fil because they do not create dust.

However, all wet blasting methods have similar disadvantages over dry abras blasting, including:

a. the availability and drainage of water; b. the production and disposal of sludge (particularly with abrasive injection); c. the extra cost of supplying and mixing a corrosion inhibitor (assuming I

specification allows the use of an inhibitor); d. he problems associated with drying largc surface areas or the higher cost

water miscible primers compared to conventional primers.

High pressure water jetting Operates at pressures sometimes in excess of 200 MPa (-30.000 p.s.i.) which can extremely dangerous. The advantages of this method are as Ibllows:

Simple to operate. Highly flcxible and mobile in use. Suitablc for removing soluble contaminants. Will remove mill scale at high pressures.

70 High pressure water plus abrasive injection Operates at pressures up to 140 MPa (-20,000 p.s.i.) which can be extreme dangerous. The advantages of this method are the sarnc as for high pressure pure wat blasting. but will also remove firmly held contamination and will create a surl'a~ profile.

,,

Air blasting will] water injection Water with or will~oul :in intlibitor is injectcd into an itir-lahn~sivc strcam.

Low pressurc water plus abrasive injection Operates at -0.7 MPa ( 100 p.s.i.). It is claimed t I i ; ~ t this technique is very controllab and will remove one c(13t o f pi~i~lt i f required. Disatlvantagcs include high cost ant1 lo cf[iciency.

go

Steam blasting, with o r without abrasive injection Operates at -0.7 M-Pa (100 p.s.i.). This method is iclcal S t ~ r surfaccs cuntaminatcd wi oil. grease, etc.. Disi~dvantages include high cost i l r~ t l low cl'liciency.

Ruane & T P OINei//

Bronze brushes mwy not be pennitred becuare rf rlre po.rsibiliy cflgulvunic corrosion. Pluriic brisiles wirh embedded abrusives ([re uvuiluble u.r (cm alrernurive.

/ Hand and power tool cleaning

Reciprocating needles

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ro

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60

NEEDLE GUN

Hand and power tool cleaning, relates to scraping, chipping, wire brushing, sanding, lo grinding and needle gunning.

This method of cleaning, although not as effective as blast cleaning, is often used for short term protection coating systems, maintenance work, or where access for blasting is restricted or damage from abrasive to the surrounding environment would occur.

Wire brushing is a widely used surface preparation method but it only cleans up an existing surface, it does not re-cut a new profile. BS 7079 : Part A1 defines standards of wire brushed finishes along with other hand and power tool cleaning methods as follows:

Prior to hand and power tool cleaning, any heavy layers of rust shall be removed by chipping. Visible oil, grease and dirt shall also be removed.

St2 - Thorough hand and power tool cleaning. When viewed without magnification, the surface shall be free from visible oil, grease and dirt, and from poorly adhering mill scale, rust, paint coatings and foreign matter.

St3 - Very thorough hand and power tool cleaning. As for St2, but the surface shall be treated much more thoroughly to give a metallic sheen arising from the metallic substrate.

St3 is usually obtained by mechanical wire brushing and St2 is usually achieved by hand wire brushing. Care must be taken to avoid over brushing a particular area causing burnishing, a condition with a highly polished surface which has an adverse effect on coating adhesion.

For safety rcasons, i t may be specified that wire brushes used must be of the non-sparking type. i.e. phosphor-bronze or beryllium-bronze.

Needle gunning A needle gull. or Jcison's harnn~er as i t is sometimes referred to, consisb of many air operated reci procating tungsten needles. It is usually preferable for the needles to have a small cross-section. Needle guns are useful for cleaning difficult surfaces such as rivet heads and welds, they also peen (hammer) and stress relieve the surface. Their disadvantages are that they can leave sharp edged craters and rogue peaks and they also have a tendency to push impurities into the surface.

After needle gunning tlie amplitude of the surface profile may be checked by the same methods used for abrasive blast cleaning if the contour of the substrate allows.

Ruane & T P 0 'Neil/

( Flame cleaning

Differential expansion - The mill scale on contact with the inlense heat expands at a faster rate than the steel to which it is attached and flakes off.

lo

The application or an oxyacetylene flame to the steel surface 10 be cleaned is an efficient method of removing rust, mill scale and other contamination. The effectiveness of the process is due to a combination of factors:

Heat penetration - The heat from the flame penetrates all the surface irregularities and removes all traces of moisture, oil, grease, etc..

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The flanie cleaning of any form of fastener, e.g. rivets or bolts, should be avoided as a loss of mechanical strength may be caused.

Dehydration - Rust is a combination of iron oxide and moisture. As the moisture is rapidly driven off the rust is dehydrated and converted to a dry powder which can be removed by wire brushing.

a/ Flame cleaning often requires three operatives who work in a learn as follows:

No.1 - flame cleans the surface, this gives a light grey appearance on the surface when finished.

I No.2 - wire brushes the surface to remove all the dry powder.

40

/ Chemical cleaning

No.3 - primes the surface; it is often necessary to apply the paint while the metal is still warm, around 40°C (which is about the maximum to which the hand can be comfortably applied).

SO

The warmth of the plate lowers the paint viscosity enabling i t to flow more easily into irregularities and also ensures that condensalion will not form on the surface.

BS 7079 : Part A l shows minimum flanie cleaning standards according to rust grades. i.e. A F1. B FI. C F1 and D FI.

60 Pickling and phospha ting Pickling is a chemical cleaning process which is widcly used i n a factory environmenl for preparing itenis such as pipes and steel plates.

70

The process usually involves immersing the steel i n a bath of hot acid such as sulphuric acid (H,SO,) wllicli has bce~i inhibited to reduce attack hy the acid on the steel. The acid dissolves a thin oxide layer at the interrace with the steel causing the rust or mill scalc to be removed.

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3. Wash: A clean warcr wash to rcrnove acid and surface residues, usually appliecl by hose or spray.

Other acids, e.g. phosphoric acid and chromic acid, are used to passivate the substrate to retard corrosion rcactlons and also to proniote adliesion. Tlle acids react with the steel to form a thin laycr on [he surface which passivates the surface and provides corrosion resistance.

Procedure (H B Footner's duplex process):

YO

I . Degrease: Re~novcs surface conlaminants such as grease and oil by the use ot' :I

suitable solvcnr, c . ~ . xylcne, usually applied I>y cloth.

2 Pickle: Total imnlcrsion in a lank ol' acid, e.g. 5-10% sulphuric acid at 65-70°C, 10 rcnlove mill sc:~lc. rusr crc., the time taken is vnriahlc and depends upon lhc type and degree of'contaniiriation. An i~iliibitor is also prcsenr i n this tank.

Ruane 6; T P O1NeiI

4. Phospllate: The technique involves a final treatment in a I to 2% phosphoric acid solution held at RO°C, for I to 2 lninutcs. This leaves a thin rust inhibitive phosphate coating on the steel surface to which the coating should be preferably applied while it is still warm, possibly after a final wash.

Hydrocarbon solvent cleaners The removal of oil or grease from a substrate using hydrocarbon solvents involves proprietary brands of degreasers which usually use solvents such as xylene, toluene and solvent naptha. Other solvents known as halogenated hydrocarbon solvents such as perchloroethane and perchloroethylene are also used.

Note: Halogenated hydrocarbons such as 1, I , I trichloroethane, trichloroethylene and carbon tetrachloride were commonly used as degreasers but their use has declined, or been completely restricted, due to high toxicity. Heavy vapours of all chemical solvents are a hazard in enclosed areas, e.g. inside tanks.

A thin film of oil invariably remains after solvent cleaning but the more solvent used and the more frequent the operation, the less residual matter here is present.

Xylene is a commonly used degreaser but its use on painted surfaces is limited due to solvent strength and compatibility considerations.

Ruane & II T P O'Nei

Some non-ferrous metallic surfaces such as copper, brass and gaivanized steel may be coated for anti-corrosion purposes but sometimes they are coated only for aesthetic reasons. Relatively reactive metals, e.g. zinc and aluminium, are often coated to prolong their effective life.

lo

3. Rinse using clean water. Preferably use power washing equipment where the situation allows.

Non-metallic materials such as glass reinforced plastic (GRP) or concrete are of'tcn coated for appearance reasons only, although if concrete is coated its effective life or time to maintenance may be prolonged.

Regardless of the reason(s) for coating the surface must be cleaned.

Typical procedure:

20

4. Sweep abrasive blasting preferred. If this is not practical, abrade using emery cloth or wire brush.

1. Remove any oil or grease by means of a suitable solvent or proprietary degrcascr.

2. Remove any water soluble contaminants using water, usually mixed with detergent (-2%).

For many non-ferrous substrates including aluminium and zinc a polyvinyl-butyral (PVB) type etch primer or a non-proprietary etchant called T-wash is usually used. The etchant used in both cases is phosphoric acid.

40

It may not be feasible to use sweep blasting as a surface preparation method with certain surfaces such as thin gauge aluminium cladding or zinc galvanising. However, using wire brushing or some other abrasion method may not always be the best alternative. Etch primers or erchants are usually on these surfaces to provide a key to the substrate.

The specification must always be consulted to determine which preparation method to use on non-ferrous substrates. For example, a specification may require T-wash ctchant to be used on urlwearhered zinc galvanized surfaces, PVB etch primers on aluminium surfaces and abrasion using emery cloth on copper surfaces.

,, It is not always a requirement to apply etch primers or etchants to zinc coatings which have a dull appearance due to an oxide layer which has formed over time due to reactions with the oxygen in the atmosphere. The oxide layer usually provides an adequate key for the coating system.

Ruane & T P 0 'Neil/

The porassium ferncyanide resr may uLco be referred ro as the porassium hexclcyano/Lrrure (111) resr.

Tests to detect surface contamination may be qualitative or quanfitative. Qualitative tests will determine whether or not contamination is present but they will not show the exact quantity, altl~ough an idea of the extent of contamination will normally be determined. There are many tests for detecting contamination but some of these require a chemist or other suitable qualified person to perfom; these tests tend to be mainly quantita~ive, i.e. a quantity is determined, e.g in mg/m2, although even this value may not be the exact amount actually present.

I Soluble iron salts Colourless soluble iron salts may be present i.n pits within the substrate after blast cleaning. If salts are present, they will accelerate corrosion causing rust spots which may in turn break the bond of any applied coatings leading to the failure of the coating system.

Some specifications state the maximum levels of salts permissible on a surface and express the quantity in milligrams per square meter (mg/m2 or mg.m").

The maximum requirement may be as low as 10 mg/m2 although other specifications may state that 30 mg/m2 is the critical level. Only quantitative tests could be used to determine whether these requirements are met.

Note: Test results may be misleading or totally wrong if chromate or nitrate inhibitors have been used, for example in wet blasting.

Potassium ferricyanide test 1 . Spray a fine mist of distilled water onto a small area of the blast cleaned surface

using a scent-spray type of bottle.

2. Wait a moment for any water droplets lo evaporate then apply a potassium ferricyanide test paper by pressing down for 2 to 5 seconds.

3. Remove the test paper and check to see i f any salts have been drawn by capil1,uy action. They show as prussian blue spots.

Bresle sample patch This is a mercury (11) nitrate (mercuric nitrate) [itration test claimed to be 95% accurate down to 10 mg/m2. (Reference I S 0 8502 : Part 6).

,,

Salt contamination meters These normally give a digital readout and work by directly measuring the ionised metal salts dissolved in a quantity of water.

Merckoquant Test This test is also known as the Eisen test and is a colormetric quantitative test claimed to be 85% accurate down to 30 mg/m2.

'01 Mill scale Mill scale is cathodic with respect to stccl. Tills mcans that if any traces of mill scale are presenl on rhe surface aftcr preparntiol~ they can accelerate the corrosion of the underlying steel and disbond. Icad~ng to thc cvcnlual failure of any coating system applled.

To test for the presence of any mill k a l e p;trtlcles left behind after blast cleaning lo BS 7079 grade Sa3 the copper s ~ t l p l r a r c ~ rcsr 111;ly bc used.

Ruanc & T P O'Neii

Procedure

A fine mist of slightly acidic copper sulphate solution is sprayed onto a localiscd area of approxirnatcly 100 rnrn in diameter. The steel turns a bright copper colour and any mill scale particles show as black spots.

I Dust The presence of dust may be determined by applying transparent pressure-sensitive adhesive tape to the test surface and then removing. The tape is examined using a magnifying glass and an assessment of the degree of dust contamination is made. Standards do exist which standardize the test conditions and the way in which the results are assessed. For example, the pressure applied to the tape and its degree of stickiness will partly govern the results. (Reference BS 7079 : Part B3).

Oil or grease 1 Simple visual assessment may reveal the presence of oil or grease, however. a cotton

wool swab wiped over the surface may reveal oil or grease which was not directly visible when on the surface. The use of an ultraviolet lamp may also detect oil or grease by causing it to fluoresce, but a dark environment is required for this method.

Another method is to drip several drops, using an eye type dropper, of a solvent such as xylene onto the suspect area. After a few moments remove some of the solvent with the dropper and drip the solvent onto a tissue or filter paper. When the solvent has evaporated any oil or grease removed by the solvent will show up on the paper as a brown ring.

I Paints may be classified in several different ways, however, one way in which paints may be sub-divided is as follows:

Liquid paints containing solvent

Solvent free liquid paints.

Powder paints.

Solvent free liquid paints and powder paints are latter developments which eliminate the need for costly and hazardous solvents.

Liquid paints containing solvents are the most common, although solvent free materials are becoming more widely used. Water based paints have been used for sometime in industrial applications, e.g. electrodeposition paints in the motor industry.

Opaque liquid paints consist of a liquid medium known as the vehicle (which primarily contains binder and solvent) plus solid pigment particles. An unpigmented paint is known as a varnish.

301 Binder

I A paint type is normally identified by its binder.

40

/ Examples of binders:

The binder is the film former, i.e. the component in the paint which forms a relatively hard continuous film. It may be thought of as the adhesive that holds the pigment and other additives together. The binder contributes mainly to the durability, provides the necessary mechanical and physical properties and provides the adhesion, cohesion and flexibility of the protective coating.

1 Acrylic

Alkyd

Cellulose

1 Chlorinated rubber

PVCIPVA emulsion

Epoxy

Ethyl and methyl silicate Vegatable oils, e.g. linsecd oil, tung oil

I Phenolic

I Polyurethane

Silicone 701 Styrene

A paint binder forms polymers when drying takes place. A polymer molecule is composed or many smnllcr parts, contributed by si~nilar or dissimilar simple molecules which arc joined together until thcre arc llundrcds or thousands of atoms in the polymer molecule. l i i s process is known as polyn~t~rrsrrlior~.

80

Polymers consist of chemical con~pounds mndc up Iron1 clemcnts of a low rnolccular i weight, such as carbon, hydrogen, oxygen and nitrogcn.

Each binder has its own characteristics, therefore a paint must be carefully selected to ensure it is able to do the work required; e.g. it would not be the right choice to coat a chemical plant with a linseed oil based paint as these paints have low resistance to chcmical attack. An epoxy or a chlorinated rubbcr based paint would bc a much bettcr clioice as these paints have good chemical resistance properties.

Most polymers are organic and nlny bc naturally occuring, or as is more usual i n modern paints, synthctic.

-A-A= A-A-A-A

Plgmenfs ore msolublc; dyes urr soluble

Linear polymer

lo

Branched polymer A-A-A-A- -A-A-A-A-A-B:

A-A-A-

Cross-linked polymer

4 0

Some natural resins are soluble in organic solvents but not in water, some natural resins classified as gum are soluble in water, e.g. gum arabic.

All binders are polymers and in the case of reversible or nun-converrible coatings, the polymer is fully formed and therefore does not undergo further polymerisation during the drying or curing process.,

Nun-reversible or convertible binders are composed of polymers which are not fully formed and which undergo further polymerisation during the drying or curing process.

M

Resins Natural resins are obtained from plant secretions or plant fossils and include lac, copals and darnmars. Natural resins may be hard brittle solids or soft semi-solids, are usually quite transparent and may have film forming properties although they are usually used to modify the properties of oils. Natural resins. quite often have to be modified chemically by heating, etc., before they are of any use to the paint industry.

60

Pigments

Almost all resins used in paint formulations nowadays are synthetic, e.g. epoxy, alkyd, vinyl etc.. these have similar physical properties to natural resins but have different chemical compositions.

,

Pigments are solids in powdered form which are derived from either chemical reactions, minerals, vegetables, 'or animals. Pigments may be organic or inorganic. Most pigments used in paints are inorganic although there are some common organic pigments. Most pigment types must be chemically inert and insoluble in the vehicle In which they are dispersed.

Oils Before synthetic resins (modern binders) made their appearance, unsaturated drying oils were used as film formers. Nowadays. their use is restricted, although they are commonly used in oleoresinous varnishes (oil and resin) for specialised uses.

Common drying oils are linseed oil and tung oil which dry by oxidation.

Paints which contain more oil than resin may be referred to as long oil paints, these produce elastic, slow drying, paint films used for decorative purposes. Paints which contain more resin than oil may be referred lo as shorr oil paints, lhese produce brittle. fast drying, paint films used for structural coatings.

Ruane & T P Oweill

Pigments basically give a paint film its colour and opacity (hiding power), but may also improve the paint films hardness and durability. Colour permanance when exposed to the environment, i.e. light, air and moisture, is also a consideration. Opacifying pigments are typically less then 1 pm per particle.

There are pigments which can apply other characteristics to a paint, e.g. anti-corrosive ( N S ~ inhibitive) properties.

Titanium dioxide is a white pigment and worthy of special mention because it is present in many paints over a variety of colours. Its main characteristics are high tinting strength and hiding power, low weight, good chemical inertness and resistance to heat.

Pigments are usually classified by colour or by the primary characteristic they afford to the paint; listed below are some pigments classified by the latter:

Opaque pigments

These inert pigments are used for the purpose of providing colour and opacity.

Carbon - black

Compounds of calcium - red, yellow

Compounds of cobalt - blue

Compounds of chromium - green, yellow, orange

Compounds of iron -brown, red, yellow

Titanium dioxide - white

Rust inhibitive (anti-corrosive) pigments:

Used in primers for the purpose oFcorrosion prevention.

Inhibitive pigments work by anodic andfor cathodic polarisation of the metal substrate. The soluble particles of some types of rust inhibitive pigment react with the moisture as it passes through to the metal making it non-corrosive. Red lead and calcium plumbate are basic and react with acidic components of the vehicle to form an inhibitor.

Red lead*

Calcium plumbate*

Zinc chromate*

Zinc phosphate

Boro-silicates

Zinc phospho-oxide

Barium metaniobate *Note: The use of red lead, calcium plumbate and zinc chromate, in most countries is banned or restricted due to high toxicity.

Metallic pigments:

May be used to give metallic finishes such as those used on cars. Zinc may be used to give anti-corrosive properties by acting as a sacrificial anode, i.e. by means of cathodically protecting the underlying steel, providing the metallic particles are in close contact with onc another. In most situations. it is unlikely that an aluminium pigment, even if closcly packed, will achieve cathodic protection.

Zinc

Aluminium

Ruane & T P O . N e i ~

Micaceous meuns mica, or u.f is tile cuse with micuceous iron oxide. having chumcrerisrics similar to mica.

Extender pigments:

More oAen referred to as extenders; these are not opaque, i.e they have no hiding power, and are used for increasing viscosity, reducing gloss, aiding intercoat adhesion and to improve the cohesive strength of the paint film. Some opaque pigments can also provide these characteristics, but the main advantage of using extenders is lower cost.

Kaolin (china clay)

Chalk

Talc

Slate dust

Barytes

Laminar pigments: Laminar pigments are small flakes which have a leafing effect when the paint dries; this means that the flakes of pigment overlap one another like tree leaves on the ground. This results in an excellent coating to resist the passage of water; the tensile strength of the coating is also improved.

MI0 (micaceous iron oxide), sometimes referred to as flaky or specular hematite, is a laminar pigment widely used in midcoats on structural steelwork and is available in many types of binder formulations. Mica, glass flakes, and aluminium flakes, are other laminar pigments which have similar characteristics to MIO.

I Solvents Usually the ability of a paint to spread over a surface is far from ideal unless the paint contains a solvent.

I with the liquid paint which will have an adverse effect on the paint film properties.

50 fuinlsdesi~ned to be solvent free may have uccepruble u~~plicutirm properties

I The important properties of a solvent are as follows:

The paints .Solvent must be volatile so that it evaporates from a coating of paint to leave a viscous film.

The choice of solvents is important because the use of inappropriate solvents can affect the drying and gloss characteristics of a paint and in some cases can chemically react

1 Sotrent power

Strong solvents. e.g. acetone, are required for complicated polymers. this enables the molecules of the paint to move more easily.

ate of evaporation

Some solvents evaporate quicker than others, also the method of application will effect evaporation; spraying results in faster evaporation than brush applied coatings. If the rate of evaporation is too quick problems may arise during application, e.g. dry spray.

Flash point

This is the minimum temperalure of the solvent at which the vapours given off are fla~nmable i f a source of ignition is introduced.

Toxicity

The toxicity of a solvent can be determined from its o c c u p n t i o r ~ a l exposure limit

expressed in pctrts p e r m i l l i o n ( p . p . m . ) . See Unit PI 2 .

A variety of' apparntux exists for measuring toxicity, a comlnon type known as the Drcteaer t n l ~ e works on a similar principle to the breathalyser.

Ruane & T P OINei/

I 0 ther constituents In addition to the main ingredients o f a paint, namely the binder, solvent and pigment, there are other constituents added for a variety of reasons, e.g. to aid the paint manufacturing process, to increase shelf life, to aid application, to aid film formation, to aid drying or curing, to repel bacteria o r suppress plant growth, to reduce flammability, and to reduce UV degradation.

Other constituents include plasticizers, thixotropes, driers, anti-skinning agents, anti-foam agents, preservatives, fungicides and bactericides.

/ Solutions and dispersions

30

a. Sugar (the solute) with water (the solvent). b. Alkyd binder (the solute) with white spirit (the solvent).

A n opaque paint is a dispersion; the pigment particles are suspended in the vehicle o r binder. The vehicle of a paint is a solution of binder dissolved in solvent; a clear varnish is also a solution.

4 0

Dispersions In a dispersion thcre is no solubility, one component, which could be a liquid or a solid. is surrounded by a liquid. There are two types of dispersions: suspensions and emulsions.

Solutions In a solution, a substance known a s the solute, which can either be a solid o r a liquid, is dissolved in a liquid known as the solvent, to form a homogeneous substance.

For example:

Suspensions

In a suspension, solid particles are dispersed within a liquid, each particle o r group of particles being surrounded and wetted by the liquid, e.g. pigment and vehicle.

If a paint was in complete dispersion each pigment particle would be completely surrounded and wetted by the binder.

In practice, complete dispersion is rarely achieved because the pigment particles group together in small groups known as aggregates when supplied by the pigment manufacturer; thcse aggregates a re not completely broken down by the paint mills during paint manufacture.

However, the paint manufacturer must break down the aggregates to achieve thc necessary degree ofdispersion orfineness of grind for the particular paint; for example, the final degree of dispersion must be high to obtain gloss paints.

Emulsions

In an emulsion, minute droplets of one liquid known as the dispersed phase, arc dispersed in a second liquid known as the contin~ious phase. T h e dispersed phasc is completely surrounded by the continuous phasc but is not dissolved by i t .

For example:

a. Full cream milk: Cream (dispersed phase) with water (continuous phasc). b. Salad dressing: Vinegar (dispersed phase) with oil (continuous phase). c . Household emulsion: PVCffVA oo-polymer (dispersed phase) with wntcr

(continuous phase).

Ruane 6; T P O I N e i ~

Drying is defincd in BS 2015 : 1992 : Glossar~~ of painf and relafed ferrns as 'The changc of a coating material from thc liquid to the solid state, due to evaporation o f solvent, physico-chcmical reactions of the binding medium, or a combination of these processes.'

When the drying process takes place during exposure to air at normal temperatures, i t is called air drying; if drying is accelerated by the application of heat above ambient temperature, but below that used for stoving, i t is termed forced drying. Application of hcat by using an oven or infra-red energy is termcd sfoving.

Various terms exist in relation to the drying of a paint film:

Dust dry - When dust no longer adheres to the paint surface.

Surface dry or sand dry - [Not a BS 2015 : 1992 term] When the paint is dry on the surface but is soft and tacky underneath. This term primarily applies to oil based paints.

Touch dry -When a very slight pressure with the fingers does not leavc a mark or reveal stickiness. Frcedonz from residrral tack is another tcrm encountcred.

Tack frce - Free from tack, cven under pressure.

Hard dry - [Not delined in BS 2015 : 1992) This term is used to describe ccrtain degrees of film hardness when tested by specified methods. The term may also be used when the drying has reached such a stage that, if desired, a further coat may be applied.

Dry to handle -The state of drying when a coated item can be handled without damage.

I Drying mechanisms I Thc types of drying mcchvnis~ns are:

50

Solvent evaporation

Oxidation

Chemical curing

Coalescence

Solvent evaporation (physical drying) Somc paints dry solely by solvent evaporation to leave a film of non-volatilc solids; but a pcrlnanenr chemical changc does not take place. This process is somc[irncs known as lacrluer drying.

I';linls which cure solely by solvent evaporation are known ;IS rrorr-co~lr~trrriblc or re~.rersiblc yainfs. These tcrlns lnean that the binder is a linear or branched polymcr whicl~ is fully formcd in the can and does not undergo rurther polyrnc~-ization artcr application. It also means that i f the paint's solvent, or other solvcnts in the case of houscliold emulsion paints, is rcapplicd to a dried coating. thc coating will rcsol'tcn.

Non-convertible paints such as chlorinated rubbcr and cellulose lacclucrs arc cxamplcs of p;~in[s which dry solely by solvent evaporation (lacquer dry).

Oxid a t' ron I';~inrs hasctl on drying oils, wl~icli includcs most alkyd and phenolic paints, dry lirstly hy solvcnt evaporation then by oxidation. This is sometilnes known as oxitlativc drying. On contact with the oxygen in the air a chemical reaction tnkcs placc - tlic pain1 polyllicrizes, with the aid ol'tlri~r-s wliich are prescnt in the paint, to I'orrn a relarivcly li;~r(l 1.1 Irii.

I'a~nts which curc by oxidation arc known as cor~verriblc or rrorr-rc.~lc,rsiblc /)trirrrs, wlilcli rncans that il' thc paints solvcnt is renpplicd ro a cured coating. ~ h c coating = ' i l l no[ I-ctllssolvc hccausc ol'thc pcrlnanent chclnical cl~angc which 1i;ls [ahcn placc.

Ruane & T P OqNei\

Paints which dry by this mechanism have complex polymers compared to reversible non-convertible paints.

Puinrs which melt when hcu( is npplied ure known us thermoplastic coatings. Coarings which du nor mc!l ufier (he applica(ion [,/hear ure known U.T thermoset coatings.

Chemical curing Chemical curing paints cure by a chemical reaction between ingredients in the pa unlike oxidation drying which is a chemical reaction between the binder and oxygen the atmosphere. Paints employing this drying mechanism dry initially by solv, evaporation, if a solvent is present, and then by polymerization due to a chemi, reaction with the curing agent.

Paints which chemically cure are convertible or non-reversible paints, and theref( have complex polymers compared to non-convertible or reversible paints.

Curing agents can be added to a paint prior to application (two-pack systems), or th can be already present in a paint and then activated by an external source of energ e.g. heat, ultra-violet light, infra-red light, electron beam etc..

The induction period is the minimum period of time during which the mixe components are left to stand before use. This is to allow for certain chemical reactior to take place. Induction periods are typically up to 30 minutes.

Orher rermr f i r inducrion periodureleadtimecllld 30

stand time.

Coalescence Paints which dry by this mechanism dry initially by water evaporation; this allows th polymers of the paint, which are fully formed during the manufacture of the polymer, t come into contact with one another and physically join together.

Acrylic elnuisions and vinyl emulsions dry by this mechanism and are classed a rtorl-cotlverrihle 01. reversible paints, although this is not very obvious in practice.

Two-pack paints are used taking into consideration the pot life and in some cases 11 inductiorz period.

The pot life is the maximum period of time after mixing in which the paint must t used; this can vary from a few minutes to a few hours.

/ Corrosion protection methods Paint systems protect thc substrate from corrosion by a combination of one or more or the following methods:

2. Passivation: Corrosion is retarded or arrested by chemical reactions between rust inhibitive pigments in the primer, and the substrate andfor moisture passing through the paint film.

20

I. T h e barrier principIe: The substrate is isolated from the environment which causes corrosion by using a coating which has low permeability to moisture and air. This may be achieved by applying a thick coat of paint or applying a paint having low permeability, e.g. epoxy, polyurethane; or even better applying a thick, low permeability coating.

40 ( Layers of a paint film

30

Paint sys tem may be single layered coatings or multi-layered coatings. A multi-layered paint system consists of a primer, at least one midcoat and a finish coat. Each coat has its own specific function.

3. Cathodic protection: This is achieved by coating the substrate with a paint containing metallic pigments - usually zinc (aluminium in some cases), which are ignoble with respect to the substrate. Cathodic protection may also be achieved by means of metal coatings such as zinc galvanizing.

I Primer The function of a primer is to provide maximum and lasting adhesion to a substrate. to provide a key for the next paint layer and, in most cases, to retard corrosion by means of an inhibitive pigment when the primer is applied to steel substrates.

M o r d u ~ ~ t means "o/u corrosive nulure", or "ttr Oire info".

Although not always practiced, it is often considered good practice to apply primers with a brush as this enables the paint to be worked into the substrate's surface, thereby providing optimum wetting of the substrate and mixing in any dust particles, thus achieving optimum adhesion. ,

Etch primers, also known as wash primers, are supplied either as single pack or two pack materials which contain phosphoric acid that reacts with the substrate and which also sometimes contain an inhibi1iv.e pigment such as zinc phosphate. This type or coating is often considcrcd as an.elchant or form of surface preparation rather than a primer in the conventionhl sense. :.

Another form of etch rype prinicr is the mordant solution. An example of this is T-Wash which waspeveloped 'by the former British Rail. T-Wash essentially consists of an aqueous sojtltionof phosphoric acid and copper sulphate.

Many ~~ecifications~'wil1 not allow etch primers to be spray applied due to thcir high toxicity. t

Midcoat Midcoats may be srandard undcrcoats or high-build coats, primarily therc to serve as a barrier to prevent the passagc ol' wacer.

Primers and finish co;~ts are otien t h i n layered coatings and are quite permeable compared to midcoats; without a niidcoat thc inhibitive pigment in the prirncr would soon be leached out. which will 1c;;b to corrosion.

Midcoats also build up thc film thlckncss to prov~de a more even surface by fillirlg iri

sl~ght surface irrcgularltlc~

0 Uumnc & TI' O'Ncill Is'ac .I 1 Y O I D 7

Ruane & // T P O'Nei

Finish The rinal coat i n a systeni gives a surface its final appearance, i.e. colour and gloss. A final coat must also have solar protective properties and, on most structural work, must have a gloss finish to also allow water to flow more readily from a surface and allow

l0l

the surface to be cleaned easily.

Types of coating system

20 General There are various ways to classify paint systems as shown in the following table:

Classification

Function

Binder type

Pigment type

Colour

Options

Anti-corrosion Anti-fouling Decorative Flame retardent Heat resistant Shop primer Moisture tolerant Road marking

Alkyd Cellulose Chlorinated Rubber PVC/PVA emuls~on

Epoxy Polyurethane V~nyl

Alulniniurn Micaceous iron oxidc Zinc rich Red oxide Z ~ n c phosphate

Black Bluc Grccn licd Whitc Ycllow

Ruane & T P OINei//

The following table extracted from BS 5493, s l ~ o w s the principle coating systems identified by their binder:

Moisture-curing polyurerhunes und high-mr)leculur-weifihl lineur epoxy resins which ore both one pack chernicul-resisrunr mareriuls. are nor included in rhe product secrions becuuse of limited expen'ence ill tlreir use ur the rinw r f B S 5491 publicurion.

Sprayed metal: bare, sealed or Zinc or aluminium metal painted

Zinc coating (except sprayed metal): bare. sealed or minted

Characteristic constituents

Zinc and/or zinc-iron alloy

I Organic zinc-rich

Inorganic zinc-rich

Drying oil type

I One-pack chemical-resistant ( Chlorinated rubber or vinyl copolymer 1

Zinc and organic binder

Zinc and silicate binder

Drying oil, urethane oil, alkyd, modified alkyd, phenolic varnish or epoxy ester plus pigment

Sillcone alkyd Silicone-modified alkyd plus pigment

drying oil type primer chlorinated rubber finish

Two-pack chemical-resistant Epoxy or polyurethane resin (including

I

One-pack chemical-resistant and

I I modificationwith coal tar) plus I

resin plus pigment

Epoxy ester or alkyd primcr with

I I pigment I

( Bitumens ( Coal tar or mineral bitumen with or 1

Two-pack chemical-resistant overcoated with one-pack chemical resistant travcl coat and finish

Sacrificial coatings s,,. . c r ~ l ~ c ~ a l ' - ' coatings contain pigments which cathodically protect the iron or steel substri~te to which the paint is adhered, these pigment particles eventually corrode thereby sacrificing themselves by corroding in preference to the substrate. In order to 11;lve this property the sacrificial pigment must be ignoblc to the material to be coated; zinc and aluminium are tile most common types of pigment employed.

Epoxy resin overcoated with chlorinated rubber plus p ig~nent

Zirrr ric4 pri171cr.r are two-pack paints contain ~netallic zinc in high concentration. A rnir~i~liurn zinc contcnt 01'90% (by weight) of the d.1.t. is oftcn specilicd.

'01 In order to work effectively the zinc particles must be held in close contact with tlicmselves and the subsuatc, therefore an efficient bindcr is necessary.

I Organic zinc rich primers usually have an epoxy binder.

Mctal coatings, e.g. zinc galvanizing and metal sprayed coatings, are principally used Sol. very long tcrm protection and d o not usually conic undcr thc category of paint .;y stcms.

eo

When a zinc rich or a zinc 11ictaI coating is subject 10 ~ii inor damngc, c.2. a scratch, a corrosion reaction will takc place which produces zinc salts t h a ~ self-seal the damagcd urea.

Inorg;lnic zinc rich primers often contain a methyl or ethyl silicate bindcr. They havc excellent licat resistance propcrtics and may bc uscd as a singIc coat system or tlley lllay be overcoated wit11 a specialised finish, c.g. siliconc sealer, ifrcquircd.

Ruane & T P 0 Neil'

I Powder coatings

10

20

Powder coatings are basically solvent free paints. They may be thermosetting or thermoplastic.

Epoxy powder, which gives a thermoset coating, is commonly used nowadays for a variety of applications including underground pipelines and domestic appliances. Each thermoset powder particle contains base and curing agent, but they do not react together until they are activated with a heat source.

The component to be coated is usually preheated, the powder may then be applied by using a fluid bed or spray technique; in both cases the powder is usually applied using electrostatic methods to achieve more uniform thicknesses and to reduce powder wastage via overspray.

After application, the coating may sometimes be post-cured in a subsequent stoving operation.

30

Note: Definitions differ between specifications, always consult the applicable specification for exact defininitions which apply.

Moisture tolerant systems The surface that requires coating may be below the dew point temperature, for example, due to low temperature gas or liquid in a piping system. In situations like these, moisture tolerant systems may be specified for use on dump su~aces.

Various definitions may be used when moisture exists on a substrate, for example:

40

I. Damp surface: Surface temperature is below the dew point but there is no detectable water.

2. Moist surface: Standing water and droplets have been removed but there is a thin film of moisture on the surface.

3 . Wet surface: Droplets and free water are present on the surface.

60

The curing rate is temperature dependent (as with the other materials), but being moisture curing the curing rate is also RH% dependent. Most figures quoted for overcoating/cure tirncs arc based on 65% RH.

Paints for use on da~iip surfaces include:

Moisture curing; e.g. one pack polyurethane.

Solvent free; e.g. two pack epoxy. ' Water displacing; e.g. some moisture tolerant chlorinated rubbers.

Water absorbing; e.g. some moisture tolerant chlorinated rubbers.

70

Moisture curing Moisture curing materials are mainly polyurethanes which cure by reaction with moisture in the air, they therefore require a minimum RH% for application rather than a maximum. This value is often quite generous being as low as 35% RH, however, a maximum may still be specified - check the data sheet.

I ~ o t enamels I

80 Immediately a can is opened and moisture is in contact with the paint, the curing reaction starts, so this single pack material has a pot life varying from 6 hours upwards. Some manufacturErs stipulate that the material must bc used within 24 hours or within one working day.

0 Kusnr L TI' O'Ncill Ixsuc 1 I .VlllN7

90 The term enamels usually a'pplles to hot-applied bitumenous materials, 1.e. coal tar and asphalt (biturncn). Enarl~els wcrc, and still are for some organisations, commonly applied to the external surfaces o f pipelines, both in tlic factory for fu l l pipe lcnglhs and o n sile for the weldetl joillts

Ruane & T P O'Nei//

The pipe is first blast cleancd or chernically cleaned, then primed with the appropriate quick drying primer. Hot enamel (-200°C) is poured (f700d~d) over the primed surface then a fibreglass inner wrap is applied, possibly whilst simultaeously applying a second flood coat. Another flood coat is immediately applied and then an outer wrap, consisting of libreglass strands impregnated with the same enamel material, is wrapped around the whole surface. This system gives an homogenous, continually bonded layer with spiral wound reinforcing. The thickness range is typically 3-4 mm.

Note: Bitumen and coal tar enamels are not compatible. They are also reversible materials and so will soften and bleed with the application oi'hydrocarbon solvents.

Pinholes can be easily repaired by heating a blade and moulding surrounding material into the void.

Tape wrapping systems

Hot applied tapes

In general, these are only used in conjunction with hot applied enamels. They havc very poor adhesion properties when applied onto smooth surfaces, e.g. plastics. The tape material is mclted by blowtorch or similar and fused to thc primed material. Thc rape is then spirally wrapped around pipes and similar usually with an overlap of up to 55%.

The tape is applied to a primed substrate and spirally wrapped around pipes and similar usually with an overlap of up to 55%. Being thermoplastic. temperature affects the ease of application and behaviour during service.

I

501 Self adliesive overwrap tapes

Cold applied laminate tape

Usually consists of an outer polyvinyl chloride (PVC) or polyethylene (PE) film to which is bonded a mastic layer of synthetic rubber or rubber modified bitumen. Interleaving wax paper prevents adhesion between adjacent layers.

Not normally used as a wrapping system on their own but used as an ovcrwrap system to hold other materials in place, e.g. tillers or grease based tapes.

These tapes are PVC or PE with a thin layer of pressure sensitive adhesive. Uscd only on smooth substrates because they will not adhere properly to rough substrates.

Grease' based tapes

Arc conlposed of a synthetic fibre bandage impregnated w~th petrolatum grease. Highly ~nouldable, llexible and can be used on any substrate prov~ding i t 1s L'rec o f loosely bonded conta~nination.

Fillers Norrnally uscd to ~nodify confours of valves and flanges etc. to facilitatc the usc o f tape systems. Typically based on petrolatum grease, bitumen and rubbcr, consideration nccds lo be given to substrate and overwrapping material compatibility.

Plastic coatings There arc Inany types of plastic used in the coating industry. c.g. polypropylene. polyctllylcne and polystyrene. Common systems include heat shrinkable materials and rnaccri;~ls wllich are applied Ilo~ then shrunk onto the component by the application of cold warcr.

Elaslon~eric coatings Elasto~ncrrc coati~igs havc cl;lstic proprties and may be considcrcd ;is syrlfhc~ic rubbcr coatings. EI;~sronleric materials include: neoprene, syntactic polyurctll:~ncs and EPDM (ctlly lcrlc pl.opy lent dicnc mono~ner).

Al'rcr ; ~ l y l l i ~ ; i ~ i o ~ ~ S ~ I I I C systcriis i11.c v~rlc;~r~isecl whilst otllcrs cornc 111 IWO-pack Sorni 2nd clicm~c;ll l v cure.

There arc a large number O C painupaint film tcsts which are carricd out, some or which may be unique to onc paint rnanufacturcr or clients specification. The BS 3900 - Methods of test for painrs - is a specification widely referred to, which covers procedures, apparatus and related information on widely used test methods for paints, varnishes and similar products. The general introduction setting out the scope of the series is indended to be read i n conjunction with each of the parts which are issued In loose leaf form and can be obtained separately:

Group A - Tests on liquid paints (excluding chemical tests).

Group B - Tests involving cliemical examination of liquid paints and dried paint films.

Group C - Tests associated with paint film formation.

Group D - Optical tests on paints.

Group E - Mechanical tests on paint films.

Group F - Durability tests on paint films.

Group H - Designation of intensity, quality and size of common types of defect: general principles and rating schemes.

30

Group G - Environmental tests on paint films (including tests for resistance to corrosion and chemicals).

Ruane & T P O'Nei/

van orangeflame is observed, the temperature is too high and overheufing h u occurred. The material under tesr should be cooled or replaced and rhe resr resfaried.

Flashpoints give an indication of fire risk and are defined as. 'the lowest temperature at which solvent vapour from the product under test in a closed cup gives rise to an air/vapour mixture capable of being ignited by an external source of ignition'.

Flashpoint determination of paints or solvents may be carried out in accordance with BS3900 part A9 using a closed cup of the Abel type.

Procedure:

I . Fix the Abel cup containing the substance for assessment into a water bath.

2. Apply a hcat source to the water bath and monitor thc temperature of the substance in the Abel cup.

3. Activate the source of ignition cvery !h°C rise in temperature.

4. The flashpoint temperature is identified when a blue flame flashes ovcr the substance being assessed.

Ruane & T P 0 'Nei l

Viscosity is a measure of a fluids rcsistance to flow.

A fluid with a high viscosity has a high resistance to flow and therefore has a thick

The S.I. unit for dynamic viscosity is the Pascal second (Pas) which is equivalent to the newton-second per sqi~nre n~ef re (N.s/n12). The old c.g.s. unit, the poise, is still commonly used.

consistency; t l~e frictional forces bctwccn thc inoleculcs are greater. The opposite is

I The viscosity of water is approximately I centi-poise.

The srudy r,j the pow r,/ liquids is known u.r rheology.

10 :

true with a low viscosity fluid.

Temperature afCccts viscosity, therefore any comparative tests must be carried out at a specific temperature, e.g. 20+0.5"C.

20

Cone and plale Rotathinner Krebs slormer

Another c.g.s. unit which may be encountered relating to kinematic viscosity is the sfoke. A fluid having a viscosity of one poise and a density of 1 glcm' has a viscosityldensity ratio of one stoke.

30

I ROTATION VISCOMETER ROTOR ENDS

The instruments used for measuring viscosity are known as viscometers of which there are many types. Viscometers in paint laboratories are usually of the rotational type and include the Krebs-stormer viscometer, the cone and plate visconieter and thc rotathinner.

A s~rnple method for rneasuring the viscosi~y of free flowing paints is by using apow cup; again therc are may types including the /SO. Ford and ZahnJow cups.

: 4- stream

Procedure for measuring viscosity using a Ford flow cup No. 4:

I . Bring temperature of paint to within 2040.S0C.

2. Level the apparatus, then with the end of one finger over the orifice of the cup rapidly fill i t with paint.

3. Allow a moment for air bubbles to rise, then draw a flat edge across the top of thc cup to wipe off the paint level with the edges.

4. Remove the finger from thc orifice and start thc stop watch simultaneously with the commencement of the paint stream. The watch is stopped when the firs1 distinctive break in the paint stream occurs.

201 5 The time in seconds is taken as the viscosity.

This procedure can be used to determine the quantity of any added thinners. There is no direct relationship between the time value obtained and the percentage of added thinners. A comparison has to be obtained by preparing a number of control samples using different percentages of thinners added to the paint taken from a freshly opened can.

A thixotropic paint needs to be worked to reach the free flowing stage, therefore the viscosity cannot be assessed wilh a flow cup; a rotation viscometer or another type of viscorneter which works the paint must be used.

Density is wcight pcr unit volurnc and is thereforc found by the following formula:

weigh' Density = -

volume

The unit used for measuring the density of paint is usually grams per cubic centimetre (glc m').

1 cm' of water = I rnillilitre = 1 gram

1000 cm' of water = I litre = 1 kilogram

The density of a paint will be higher than that of water; the density of a solvent will bc lower than that of water; the density of a curing agent may be higher o r lower than that of water.

DENSITY CUP

Procedure for measuring density using a 100 cmQensity cup:

I . Weigh the cup to the nearest decigram using a laboratory balancc with a 1000 g capacity and n sensitivity of kO.1 g.

2. Rc~novc tlie cover and fill with paint to within 2.5 mm of the brini.

3. Carefully replace the cover s o that air and any excess paint is expelled through tlie VCII t .

4 Wipc off any surplus paint from the cover then reweigh.

5 Dctcrriiine the weight ol' the paint by subtraction.

0. Dividc weight by 100 if the density in glcm'is required.

This proccdurc can be applied to determine the quantity o f any nddcd thinners. Tlic wcigllt ol' 3 sample of paint taken from a paint kettle could be compared with control saniples which havc been prepared by adding di ffcring percentages of thinners to the paint taken I'ro~n a freshly opened can. Therc is a relationship bctwcen tlic obtaincd wcigllt arld thu percentage of added thinncrs if' thc prc-mixed density of' thinncrs and tlcnsity of paint is known.

11 1s also poss~hlc using this proucdurc to delcrniirlc whether two-pack palnts Iiavc bccrl ~ninc(l ~n ~ h c correct proportions.

Relative density Relative density or specific gravity is the density of any substance compared to thi

lo density of water:

dcnsity of r Specific gravity (SG) = density of water

Because the density of water is lglcrn' the figure obtained from the SG formula will be the same as that obtained from the density formula, the difference is that the answer fol the SG formula will have no units, i.e. it is a dimensionless ratio.

" Example formulae I . What is the density of a paint if 5 litres weighs 7.35 kg?

weight a. Density = -

volume 40

7.35 kg b. Denriry = -

5 litres

7.35 x 1000 gronts C. Density =

5 x I000 crtl"

I d. Density = 1.47 g/cm'

60 2. A two pack paint is mixed at a ratio of seven parts base to two parts curing agent

the densities are 1.59 g/cln7 and 0.78 g/cm' respectively. What is the density o paint after mixing?

a. 7 parts base 1.59 x 7 = 11.13

70 b. 2 parts curing agent 0.78 x 2 = 1.56

c. 9 parts combined 11.13+1.56 = 12.69

d. Density 12.69 + 9 parts = 1.41 g/crn'

Note: SG would be 1.4 1 80

Ruane & T P 0 'Nei l

The wet film thickness is taken immediately after a coating has been applied so [hat any deviation from the specified thickness range can be immediately rectified while the

Tlie w.fir. is ~omerinrcs recorded as rhe averuxe between rite lusr r o u ~ ~ i l i t t ~ roorh and rlrefirsr nom-rouching roorh.

'0

COMB GAUGE

Q

paint is still wet, thereby reducing the amount of dried coatings which are outside the specified thickness tolerances. Also any calculations based on volume solids will be meaninglcss if a lot of solvent has evaporated.

The wet film thickness may be found by using a comb gauge or an eccentric wheel.

' scale

Procedure for measuring w.f.t. using a comb gauge

I . immediately after application of the paint, the comb-gauge should be placed firmly onto the substrate in such a way that the teeth are normal to the plane of the surface.

2. The gauge should then be removed and the teeth examined in order to determine the shortest one to touch the wet paint film. The film thickness should be recorded as lying between the last touching tooth and first non-touching tooth as shown on the tooth calibrations marked on the gauge.

3 . At least two further readings should be taken in different places in order to obtain representative results over the lull coated area.

/ The wet film thickness may be found by calculation:

volume w J t . = - area

Ruane & T P 0'Nei//

( Thcrc arc four nlcthods of dctcrrnining tllc dry film thickness of a paint: '

( non-dcstructivc tcsr gauges

1 destructive test gauges

I Non-destructive test gauges

ro

Measuring the d.f.t. directly with a non-destructive test gauge is the most widely used ZOI mcthod; therc are a variety of gauges availablc with various scale ranges:

tcst panels

calculation

Magnetic film thickness (banana) gauge The harrnrla gauge, as it's most widcly referred to. may only be used for measuring thc thickncss of non-ferromagnetic coatings applied over ferromagnetic substra~cs. Prior to usc, thc gauge must be calibrated.

30

I Scale wheel \

magnetic film thickness (bannr~a) gaugc

pull-off gauge or Tinsley per~cil

magnetic horseshoe gauge

eddy current/electromagnetic gauge

Ferromagnetic substrate ' MAGNETIC FILM THICKNESS GAUGE

I Cal11~r;ltron proccdurc:

I . Choosc a magnetically insulated sllirn of known thickncss, close to thc thickness of' tllc paint you cxpccr to find, c.g. don't clloosc a 25 lrrn s l l i~n to ci~libratc i f ' yotr cxpccl thc contine ll~ickncss 10 bc in cxccss of 300 pm; this will rcducc tllc accuracy.

2 Place thc shirn on thc samc subs~ratc surfilcc finis11 as tllc surlbcc finis11 on wllicll tllc paint to be nleasured is atraclled, e.g. if thc paint is on a blasted surfacc. calibrate the gaugc or1 a n uncoatctl blastcd surfacc.

"

90

3. Place the magnet onro tllc shim and press l'irrnly on tllc irlstrun~cn[, wind tllc scalc wllcel forwards (away fronl ourse elf) until the magncl is definircly attachcd 10 the shim/substratc.

4 Gradually wind thc wllccl backwards slowly until thc nlagnct dctaches itsclf. A1 1111s point, rnovc the cursor on tllc instrument to tlle thickncss of the shim as shown on rllc scalc wheel. Will1 sorne instruments the sc;llc i[sell'must bc nlovcd to line up will1 a fixcd cursor. Whcri uslng the Iattcr type ol' instrunlcnt, ro1;llc the wllccl 10 :a/.[> ro locate tllc poslrloll of' 11lc scalc adjustor.

Ruane & T P O.Nei/

( Pull-off gauge This typc of gauge may only be used for measuring tlre ~hickness of non-ferromagnetic coatings applied over ferromagnetic substratcs. Thcy are not vcry accurate comparcd to the other non-destructive test gauges.

10

The pull-off gauge, or Tinsley pencil as it's most widely rcfcrrcd to, consists of a magnet at the tip of the instrument which attaches itself to the coated substrate. The gauge is then slowly pulled away from the coated substrate at normal incidence until the magnet detaches itself, at this point the indicator on the body of the gauge is read (you have to be quick because the magnet and indicator arc spring loadcd!). Calibration is required before use.

Magnetic horseshoe gauge The magnetic horseshoe type gauge works by measuring the change in magnetic flux between the cwo poles of a magner, the change in magnetic flux depends on the coating thickness. The accuracy of these instruments is clnimcd to be a10% and as with the other magnetic gauges, may only be used For measuring the thickness of non-ferromrrgnetic coatings applied over ferromagnetic substrarcs.

Eddy current/electron~agnetic gauges The rnost accuratc of rllc nun-destructive gauges for nlcasuring d.f.1. are tllc eddy current and clcctromagnetic gaugcs of which rhcre are ni:iny types. 11' c:illbratcd correctly, accuracy is likely to be within 25%.

Eddy current gauges are used on non-ferromagnetic conductive substratcs, electrornagncric gauges are used on ferromagnetic substrates such as ferritic stcel.

Many eddy curren~/electromagnetic gauges also have statistical capabilities and sormc will download arrd irpload informalion from computers.

Destructive test gauges Dcstructivc tcst gauges cut into thc paint til~ll ;111d should therel'orc only be uscd wllcrc necessary duc to tlic cost of repairing the da~rlagecl coating.

They are sornetimcs used on paint lilrns containing M.I.O. pigrnont; M.1.0. 1s ferromagnetic and tllercrorc non-dcstructivc ~ c s t gauges, which rcly on a non-maglietic coaling. canrror bc used.

The pair11 i~~specriorr gclrigr (I'.I.G) is onc such cypc of destructive test gaugc. A small vcc shaped c l l a ~ ~ r ~ c l is cuc illto tllc coating nc :I I'ixcd angle govorncd by a curtcr hull1 irlto tllc Sallgc '/'lie \vi(l111 01' 1111: c11;lnrrel is 111e11 I T I C B S U ~ C ~ on a p r ;~ t i c~~Ic scale I>Y nieans of ;I microscopc wli~cll is again built inlo ~ h c i~istrument.

Orhcr tlescructivc ~liick~lcss g ; ~ ~ ~ g c s are tlic S t r l ~ o : ~ rfrickr~e.~.~ clrill (11- Erit./rsor rfric.k~rc~.\..\

Ruane & T P O'Nei!

10

Test panels Test panels, e.g. metal plates of a known thickness, rnay be used to measure the d.f.1. indirectly, by coating them in the same way as the work being carried out and measuring the d.f.t. with a rnicrorneter.

20 Calculation The d.f.1. may be assessed indirectly by measuring the w.f.t. of the pain^, and providing the volume solids (v.s.%) content of the paint is known, calculating t h e d.f.t. as follows:

30

I volu~t le d . t v J t . = - area

Example:

What would be the d.f.1. if 15 litres of paint with a volume solids content of 44% is used to cover an area 12 rn x 7 rn?

To lind d.f.t.:

50

~ v ~ f I. i r rrnl ,4p1vetr r /~ rc i .~h- 111

rhr q~rcsrror~. /lri*refi~re r~rrrsr 6cfi~1111d l>y C U I C ~ I I I ~ I I I ~ I ~ I .

44 x ? c . [fJ:t. = -

100

TO lind ~ . f . t . :

60

e. w.f.t.= I5 litres

12 m x 7 n~

Converr u l l cl.i.crrr~l: urlirr ro cilnlnlr>tr III I I I .V. I r r.111

'0

r. w1.t . = 15 x l000cm' 1200 cm ~ 7 0 0 c111

15 cm g. \ v j . t . = - 840

80 i . tv.f.i. = 179pm

Return to d.f.t. formula:

Ruane & T P 0 'Nei/!!

Adhesion failures more often occur between the uncoated substrate and the primer duc to inadcquatc wctting of the substrate which may be as a result of insufiicicnr surfz~cc preparation, insufficient dust removal after surface preparation or contamination.

All paints within a system should have compatibility between coats and with the substrate. It is advisable to obtain all the components for a paint system from one manufacturer otherwise it may not be possible to guarantee the system; when compatibility is lacking it is often the adhesion which suffers.

Paint system

\ Cohesive failure

/

Substrate

(between primer and substrate)

Vee cut test With a sharp knife, cut a vee using approximately 12 mrn cuts forming a 30" angle. through the paint film and down to the substrate. Insert the tip of the knife blade under the tip of the vce and attempt to lever the paint away from the substrate. If the integrity of the coating is sound it should not peel cleanly from the surface

Cross-cut test (cross hatch test) Using a sharp knife or multi-bladed cutter. cut 6 lines vertically and horizontally. 2.0 mm apart, to produce 25 squares. Cover the area with adhesive tape and snatch off; the amount ol' segments remaining nlay on the tape may multiplied by four and then given a percentage value or a value may bc given based a scale in accordance with thc applicable specification.

The tapes dcgree of stickiness w ~ l l be relevant to this test and thc number and sizc of the squares may vary, therefore always consult the relevant specification for precise instructions.

X-cut tape test A sharp kniie or similar is used to rnakc an X shaped cut with the slrlallcr anglc between 30" and 4.5". The cuts lilust 1x2 made down to the substrate in a sirlglc action and arc matle approximately 4 0 mln in length. A piece of specified pressurc sensitive tape approximately 75 mm long and 25 mm wide is placed over thc cut ;1nd pressed down in [he central area first using finger. An eraser on the end o f a pcncil I S then used to I.irrnly rub the tape s o full adhesiorl is achieved. Within I to 2 minutes thc tapc is pullet1 ol'l' rapltlly at an anglc as closc to 180" as possible. The X-cur area I S then exam~ncd i~ntl the adhesion is ratcd using a scale from 5A = no pceli~rg or rot)roval through ro ()A = rcpnloval beyotrd rlrc~ trretr clj'rhe X.

0 Hua,nr ,C TI' O'Ncsl l 1.si,c 2 2IIIZNL

Ruane & T P owill

Dolly test A more technical adhesion test, the pull-off adhesion test or dolly test, may show:

adhesive failure between primer and substrate (most likely);

adhesive failure between paint films;

cohesive failure within an individual paint film.

"f$\ Load adiustment

Load indicator

Dolly puller - Paint film

Substrate -p

-1 PULL OFF DOLLY TEST

/ Procedure for carrying out pull-off adhesion test:

I 1 . Clean and degreare the surface to be tested and the dolly contact surface,

Alrerrlcrrive cldhcsivcs ore 50

possible. see rest procedirrc slrce1.c.

2. Roughen both surfaces with finermedium grade emery cloth.

3. Mix regular araldite and stick dolly to the surface, leave for 24 hours at 2SaC.

4. Cut paint around the dolly down to the substrate using special cutter.

M)

1 Hydraulic adhesion test

5. Attach pull-off instrument and apply pull-off force.

6. Take reading from position of cursor when dolly detaches itself. Values will typically obtained in either MPa, N/mrn2 or p.s.i..

,,

This test uses a s~mi la r princ~ple to the dolly tester, but usually gives more accurate results. The dollies used are reusable and contain a hole down their centre throl which a hydraulically operated rod nppl~cs force directly to the coated surface in or to pull the dolly away Srom thc surface. Thc opposing force IS supplied by the cnc the adhesion testcr which grips [lie top o f thc dolly.

A minimum pull-off value for the paint type used should ideally be specified in specification(s) for the work being carried out. In the absence of such criteriz minimum pull-off value should be obtained from the paint manufacturer who sho also state categorically whether or not all values less than the minimum pull-off va are deemed a failure.

Ruane & T P 0 'Neii

Holiday detectiotl or pinhole detection is an operation which detects any holes/holidays in a coating or wrapping; the instrument used for this is known as a holiday detector or pinhole detector. Substantial lack of thickness and inclusions in the coating may also be detected in some cases.

Holiday detection must not be cam'ed our on wet surfuces or in the ruin. 20

Holiday derecrors should be checked throughour the working ahy 10 ensure correct set up.

Visual inspection in addition to holiday detection is still a very important part of inspection.

There are various types of holiday detector, some used for thin paint coatings, e.g. the wet sponge type, whilst others may be used for coatings over 25 mm thick, e.g. high-frequency spark testers. For coatings ranging from approximately 0.5 mm to 4 mm thick, AC, DC or pulsed DC holiday detectors, usually powered by a 6 volt battery, would normally be used.

I High voltage holiday detectors

Voltage selection Prior to carrying out holiday detection the correct voltage must be selected because too much voltage may indicate the presence of holidays when they do not exist, or really excessive voltages may even bum a hole into the coating. Not enough voltage may result in holidays not being detected.

The volt meters or voltage settings on holiday detectors should be checked for accuracy by using a method recommended by the holiday detector manufacturer. This may involve using a calibrated volt meterlmulti-meter or proprietary calibration voltmeter supplied by the detector manufacturer.

Correct holiday detection voltage is governed by the thickness and dielectric strength of the coating. The method to use for selecting voltage should be specified for each type of coating.

50

When relatively thin coatings are being tested, e.g. fusion bonded epoxy coatings, i t is usually necessary 10 have a fine scale on the machine, e.g. 0 to 5 kV for accurate voltage selection. For thicker coatings 0 to 20 kV is normal.

I f is preferuble ro enrure rhe courtd srrucrure is properly eanhedby rcsring 60

repuir which wifl hove ro be mode on the pinlrole. ( operation

The correct voltage is ideally determined by detecting the presence of a known pinhole which has been induced diagonally through the coating to bare metal. However, the voltage is normally selected by measuring the coatinglwrapping thickness and applying

/or rhe presence O ~ U

known pinhole. This nuy nor be permirred due ro the

When operating a holiday detector on a coatcd structure, an earth wire from the main .

unit is either clipped to the structure or trailed along the ground. If the earth lead is to be trailed along the ground, the structure must be earthed, usually via a crocodile clip to a wire with a metal spike attached which is hammered into the ground.

a fo&ula, e.g. 125 V per 25 pm of thickness (same as 5 k~ per mm). or f o i ~ b i i n g other specification requirements.

The maximum travel speed for brushes or coils may be quoted in specifications. e.g. 300 mmtsec.

80

When the brush or coil comcs into contact with a holiday, a spark will jump across between the gap which completes the circuit. One or more of the following indications will warn the operator of ~ t s presence:

a. The kV dial will drop. b. An alarm will sountl, e.g. a tileeper. c . A light will come on.

The electrodes (brushes) used, which arc attached to the end of an insulated hand stick, are normally of the wire brush type although carbon impregnated neoprene brushes also exist but are not as effective. Spring wrap around coils are commonly used on pipes.

0 Runnc L TI' O'Ncill lauc 3 l 3 A l l N 7

Ruane & p 0 weill

When a holiday is detected it should be markedlcircled with a waterproof marker, but the marking should be sufficient distance from the holiday so as not to interfere with the adhesion of the repair.

''1 Wet sponge pinhole detectors Only low voltages are required for these instruments bccause water, sometimes containing a wetting agent such as washing up liquid, is used as an electrolyte to conduct the current from an electrode (wet sponge) through a pinhole to the conductive substrate.

20

There is no hard and fast rule for voltage to use with these instruments but i t is generally accepted that up to -300 p n the 9 V setting i s adequate; up to -500 pm would require the 90 V setting. The specification or written instruction should state the voltage to be used.

Water is used to wet a sponge which is connected to the positive terminal on the test instrument. When the sponge passes over a pinhole, the water is drawn into it, which allows the d.c. current to pass through to the substrate and back along the return wire to complete the circuit.

30

Some wet sponge pinhole detectors have a variable voltage setting between 9 V and 90 V. whereas others have only a single setting. e.g. 9 V.

Nuane & T P O1Nei/

I General

I BS 3900 : Part A I - Merhods of ns t s for paints. Sampling. (Same as EN 21 5 12).

10

( Generally, samples may be taken and analysed at four stages:

Sanzpling refers to taking paint samples for analysisltesting and is concerned with taking correct samples, ensuring correct identification of the samples and maintaining the samples in correct condition until assessed.

I . During manufacture - taken from the final manufacturing vessel.

2. During canning (drums, barrels, tanks also qualify).

/ 3. On delivery to purchaser - in which case the material should be unaltered.

4. At the point of application - to ensure adherence to manufacturer's recommendations (data sheet).

30~

For items 3 and 4 an independent laboratory may be used for analysis, e.g. to determine density, viscosity, thinner type used etc..

When taking samples at the application point, e.g. on site, the sample as supplied is termed sample A, the sample taken at the application point is termed sample B.

( The following points should be noted during sampling:

The paint should be thoroughly mixed to provide a homogeneous sample. The sample should be m l y representative, i.e. not confined to surface areas of the batch. Two types of apparatus will be needed for mixing and taking the sample. Preferably broad bladed stirrers or mechanical mixers and special sampling tubes or dip cans. Containers should preferably be of metal or glass. Metal containers should be uncoated internally with tight closures. Containers should have closures which are not affected by the material, e.g. by solvent attack. All sampling equipment should be scrupulously clean and dry so as not to contaminate the sample. Take into consideration safety requirements, e.g. the material under test may be toxic or Flammable. Method of sampling is related to type of material, e.g. liquid, highly viscous or powder products. When sampling from bulk storage, several small samples from differing depths and locations should make up the representative sample. For iten 3 above, the number of samples taken would largely depend on the

number of containers in a delivery. BS 3900 : Part IA recommends f i where n = number of containers. Undamaged, unopened containers would normally be chosen unless otherwise specified.

i. Labelling and sealing of samples should be done as soon as possible and information on thc label should include the I'ollowing:

I ~ 1. 11. ... 111.

iv. v. vi. vii. viii. ix.

Manufacturer's nanie/product description. Quantity and olher dctails of delivery. Batch numlxrs or othcr reference, e.g. tank nulnhcn. Date of manufacture and dale sample takcn. Tohl nunihcr of samplcs takcn. A rcfcrcncc nu~nLxr for thc siumple (for hulk dclivc~y) Tie namc of thc consignor. Thc place whcrc s;umplc is to bc laken. N;unc ol's:ui~plc~..

Salnples should be analysedltested as soon as possible and stored according to manufacturer's rcconirncnda~ions.

Reporting The sampling report should ideally contain the information given on the labcl and refer to BS 3900 : Part Al (EN 21512), or other specification used. Any abnormalities should be noted, for example:

a. Container defects. b. Visible foreign matter. c. Abnormal odours. d. Abnormal colours. e. Errors of labelling etc.. f. Presence of skin, settling etc.. g. Any difficulty in re-incorporation.

Information on the tests conducted and the results also requires recording, but the details will depend on the tests conducted and the requirements of the specitication.

The coating specification should always state the weather conditions in which a coating can or cannot be applicd. A typical painting specification extract is as follows:

( 'It is not pcrmissiblc to apply paints when the following conditions apply:

I During rain, snow. or high winds.

Relative humidity (RH%) and dew point

10 When the air or metal temperature is not at least 3OC above the dew point temperature.

When the air or mctal temperature is below 5°C.

When the relative humidity is above go%.'

30

rise in iemperuiure

Definitions Relative humidity is the amount of water vapour in the air expressed as a percentage. compared to the amount of water vapour which could be in the air at the same temperature.

The cupaciiy of u i r io hold

wuier doubles every 1 1 "C

Ute i r u ~ ~ s p o r i of mercury

I J ~ crir i.r I I ~ I perrniiled,

ihereforr cololrred trlcolrol

in gl(r.rs ihern~o~rleler.r nltr!

l ~ e .r l~ccif iedfir work w/~rc.lr

111vo1ve.r equilm~eni bei11,~

~rtrn.rpcwled by trir.

The higher the air temperature the greater the amount of water vapour which can be held in it.

The dew point is the temperature at which water vapour in the atmosphere would form condensation. Therefore, if the temperature dropped to the dew point temperature the relative humidity would rise to 100% and condensation would be formed on any objects at, or below, that temperature.

1 Measuring R.H.% and dew point Both relative humidity and dew point are measured using a h y g r o r n e l e r of which there are many types.

I. Aspirated hygrometers a. The screen h y g r o r n c r e r and Masons hygromerer are static types which rely on a

natural airflow over a wet wick. b. Assman and psychrociyne h y g r o m e f e r s are also static types which work by a fan

driven air supply over a wet wick. c. Whirling hygrometer is a portable and dynamic type which operates by

physically moving a wet wick through the air.

2. Dial hygrometers come in two main forms: hair and p o p e r . Hair hygrometers operate by expansion and contraction of hair, usually human (treated), and are extremely accurate and fast in operation. Paper hygrometers also work on absorption but this tinlc the absorbtion propertics of paper.

3. Digital hygrometers are split inlo LWO categories: (1) RH n r e f c r s which give digital readouts of RH and DP only and ( 2 ) t h e r m o - h y g r o m e t e r s which give a digital readout of RH, DP and ambient dry bulb temperatures.

The whirling hygrometer, or psychrcl17reter, is the most common type used by coating inspectors consisting of two mercury-in-glass thermometers set sidc by side in a frame which is provided with a handle and spindle s o that the frame and ~hcrmometers can be rotated quickly about a horizontal axis. The bulb on one of the thernionietcrs, callcd the rver bcdb ~ h e r c t t o n r e r e r . is covcrcd with a closely fitted cylindrical cotton wick, the end of' which dips inlo distilled watcr or clean rainwater contained in a small cylinder attached to the end of the frame.

T i c Irarnc is rotated by hand as fast as possible for at lcast 90 seconds, or as otherwise specified, so that the bulbs pass thr"ugh the air at least 4 ms.'. This causcs the water to evaporate from the wet bulh. The wet bulb cools down to a constant w e f bulb f e r r l p c r a r r i r c due to the evaporation ratc of water from the we1 wick. Always read the wet hulb temperature bcl'orc tlic dry bulb temperature ~~nmcd~atc ly after rotation.

171c d r ) Irrrll~ te~~r /~cr t r i l t re rs I I I I I I ~ I I U ~ I ~ s ~ ~ ; " ; ~ ~ 7 0 ' N c i ' '

I V ~ I I ~ ~ ~ ~ 1 1 1 1 /[tt.lor P8-1

Repeat the operation until consecutive readings of each bulb temperature agree tc within 0.2"C.

[ f i t is 100% relative humidity the wet bulb will be the same temperature as the dry bulb, because no evaporation can occur, i.e. the air is saturated. If the wet and dry bulb temperatures are the same, the current temperature is the dew point.

The relative humidity and dew point cannot be read directly from the apparatus, hygrometric tables or special slide rules must be used. Hygrometric tables are more accurate in the 90% RH rezion and above.

Metal temperature The metal temperature may be measured with a magnetic temperature gauge, sometimes known as a limpet gauge, or electrical contact thermometer.

Ruane & I- P 0 'Nei l

I Brush application

lo

There are many types of brush which may be used to apply paint; theflatpaint brush is the most common type encountered in the UK and in the USA. The oval type tends to be favoured in continental Europe.

Brushes may havefillings of the following types:

20

Brush applied coatings often do not have the uniformity of thickness usually encountered with spray applied coatings, but they do not produce spray fog or overspray, i.e. there is less of an environmental hazard, less wastage and less spotting etc. on nearby structures.

bristle, i.e. hogs hair

horsehair

natural fibres

synthetic fibres

mixture of above

30

Brushing also worh a paint into a substrates surface, which gives optimum coverage and mixes in any dust particles, thus helping to achieve optimum adhesion.

Bristles have a natural taper allowing the brush to maintain its form, they also have scales along the length of each hair which allow the brush to hold more paint. Bristle brushes are usually high quality brushes and are quite expensive.

Roller application Roller application is a quicker method than brush application and is useful for large flat areas, but unlike brush application, the paint does not get worked into a surface to the same extent and there is also a lack of uniformity in film thickness. Roller application is not permitted in certain specifications for certain work.

Curved rollers exist, i.e. for pipes; some types of roller have a paint feed via a fluid line connected to the handle.

Spray application Spray application produces production rates well in excess of that achieved by brushing and is therefore a very common paint application method.

For a paint to be sprayed successfully i t must first be atomised, i.e. it must be broken down into very fine droplets. Atomisation is achieved by both the conventiotlal spray and airless spray application methods but by different mechanisms in each case.

Conventional spray The paint is held in a container attached to the top of the gun in the case of gravity feed: underncatli the gun in the case of suction feed; or remote from the gun i n the casc of pressure feed.

Pressure fed conventional spray guns are able to cover much greater areas without the need continually lo refill the container and are therefore the most common typc of conventional spray systems encountered. Two lines feed the spray gun: one carrying the paint at a low fluid pressure, usually under 20 p.s.i.. and the other carrying an air supply a1 a pressure of approximately 40-75 p.s.i.. The air supply leads to an air cap on the gun and blows onto the paint stream as i l exits the nozzle resulting in very finc atornis;ltion.

I Airless spray

The unpressurized container containing the paint is remote from the gun; the paint is sucked i n using a fluid pump and Fed to the gun by way of a special reinforced high-pressure fluid line. A compressor supplies thc air up to approximately 100 p.s.i. to the fluid pump; this air inlet pressure is adjustable. The fluid pump multiplies the pressure by a ratio governed by the pump, e.g. a 35: 1 ratio pump supplied with an air pressure of 100 p.s.i. would lead to a fluid pressure of 3500 p.s.i. (35 x 100).

,,

In addition to conventional compressors supplying compressed air, other methods exist to achieve the fluid pressures necessary for airless spray, e.g. the diaphragm pump and the electrical pump, both these supply hydraulic pressure.

One line feeds the spray gun carrying the paint at a pressure typically between 2000 and 4000 p.s.i.. There is no air cap on the gun, hence the term airless. The paint is atomised by forcing it through a small orifice at high pressure; when the paint meets the air i t splits up into fine droplets due to the air resistance

The orifice size governs the throughput of paint whilst the orifice angle governs the size of the pattern.

,,

Typical requirements for tip orifice sizes used with airless spraying are as shown in the

The spray tips on airless spray guns are usually lined with tungsten carbide, some have the advantage of being fully reversible by turning a lever 180" to clear out any blockages in the small orifice. There is also a tip known as a titan rip which has an adjustable hole size.

table:

Paint type

Chlorinated rubber

Using airless spray equipment can be very dangerous due to the high fluid pressure; operatives must always adhere to thc Following:

High build epoxy

Zinc rich ~a in t s

Use tips designed for airless spray.

Use fluid lines in good condition designed for airless spray.

Ensure there are no kinks in thc linc.

Ensure the safety catch on the gun is sct whenever the gun is put down.

Never point the gun at anybody or yourself.

Ncver attcmpt to change o r clca~i nozzles whcn thc fluid is pressurized, i.e. shut off the pump and open thc prcssurc relief valve, whilst safety catch on the gun is set.

Ensure the equipment is earthed to prevent static shock.

Wear an air fed helmet.

Tip size

13-2 1 thou"

Airless pressure (p.s.i.)

2400

17-23 thou"

17-23 thou"

3 000

2800

Ruane 6; T P OINei//

Electrostatic spray This method of paint application requires the use of a special spray gun which applies a charge to the paint when applied. The article to be coated is earthed so that the charged particles are attracted towards it; when an area on the component has been coated to a particular thickness there is less of an attraction, due to an insulating effect the coating has, although the paint may still be attracted by uncoated areas on the article which may not be in the direct line of the application nozzle or nozzles.

This typc of application results in uniform coating thicknesses with a substantial reduction in overspray. Electrostatic spray and other electrostatic application methods are widely used in factories for coating all types of components including pipe, fridges, washing nlachines, radiators etc., using both liquid and powder coatings.

Conventional s

Maintenance

dipcoaling

padding

hot-spraying

spin rotating

flow co;iting/curtain coating

70

necessary, although can handle relatively high viscosities.

More required; especially tips, equipment is more sophisticated.

Other methods of paint application Otlicr neth hods of paint application includc:

that flow well can be sprayed.

Less required; equipment is more basic.

Ruane & T P O'Nei j

I Galvanizing

Sherardizing Used for fittings, fasteners and small items wllich arc likely to be distorted by hot-dip galvanising. Sherardizing is particularly suited to threaded components where only a small change in dimension is acceptable. The items are first degreased and pickled then tumbled for a few hours in hot zinc dust at a temperature just below the melting point of zinc. Coating thicknesses of approximately 15-30 p are typically achieved.

,,

Calorizing Same principle as sherardizing but using aluminium powder.

Used for structures. fittings and cladding. Thc components are degreased, e.g. wit11 warm caustic soda, acid cleaned, washed, Huxed with ammonium chloride then immersed in a bath of molten zinc between 420-450°C to achieve a coating thickness of approximately 85- 130 pni.

Anodising An electrolytic method of coating aluminium with a dense oxide. The component to be anodised is dipped into a bath of weak acid (usually sulphuric) and oxidation is induced electrically. For adhesion of subsequent paint films, etching may be required.

Electroplating The plating of small parts by the electrolytic deposition of metal, e.g. zinc, from metal-salt solutions. Coating thicknesses of up to 25 pm are usually applied.

( Application is normally carried out using onc of the following methods:

50

Hot metal spraying Metollisation, or the method of hot spraying one metal with another, is a widely used system for preventing corrosion of metal structures. The most common sprayed metals used are aluminium and zinc.

2. Electric arc system. The wire is used as one electrode (similar to the welding process), the energy frorn the arc melts the wire and the resulting molten metal is blown onto the substratc by means of an air jet. The arc method of metal spraying is now widely used for mechanised applications, e.g. production lines, where

60

thousands of componcnts of idcntical shape are to be coated.

I. Powder fed system. The coating metal is supplied in fine powder form and blown through a heat source onto the substrate. This is a very wasteful method which often requires a recycling facility.

3. Wire and pistol systenl. This is the most common method of metal spray application in use. It consist ol'a hand held gun with an air powered motor which draws in wire through knurled feed rollers inlo an oxygedfuel gas flame where the metal is melted. This moltcn metal is then projected onto the preparcd surface by the products of combustion augmented by an air blast from the compressed air driven motor.

Metal sprayed coatings arc often sealed to prolong their lifc due to their porous nature.

Ruane & T P O'NeNe,/

I I Thc prcsence of particles of gel, flocculalcd rnatcrial or foreign rnatter in a coclting

-

( material or projecting from the surface of a f i ln~

1 The following tcrrns have becn extractcd from BS 2015 - Glossary ofpain/ terms.

Bi ttiness:

I I Bleeding:

The process of diffusion of a soluble coloured substance from. into or through a coating material from beneath, thus producing an undesirable staining or discoloration.

Blistering:

The formation of dome-shaped projections or blisters in paints in the dry film of a coating material by local loss of adhesion and litling of thefilm from the underlying surface.

lo

I I NOTE: Such blisters (nay contain liquid. vapour, gar or crystals.

NOTE I: The term seedy specifically denotes thc presence of bits that have developed In a coating matenal during storage.

NOTE 2: The term peppery is sometimes used whcn thc bits are small and unifortnly distributed.

A deposit resembling the bloom on a grape that sometimes formson the glossfilm of a coating, causing loss of gloss and dulling of colour.

Chalking:

40

I Cracking:

The formation of a friable, powdery layer on the surface of the film of a coating material caused by disintegration of the binding medium due to disruptive factors during weathering. NOTE: Cholking can be considerably affected by the choice and concentration of pigment.

Cissing:

50

Generally, the splitting of a dry paint or varnish filtn, usually as a result of ageing. The following terms are used to denote the nature and extent of this defect:

The formation of small areas of the wet film of a coating material where the coating nrcrrerial has receded leavinz holidqs in thefilm.

I I Hair cracking: Cracking that comprises find cracks which may not penetrate the

top coat; they occur erratically and at random.

Checking: Cracking that comprises fine cracks which do not penetrate the top coat and are distributed ovcr the surface giving the semblance of a small pattern.

I Cracking: Specifically. a breakdown in which the cracks penetrate at least one coat and whicli may be expected to result ultimately in complete hilure.

jO1

Crazing: Cracking that resembles checkirrg but the cracks are deeper and broader.

Crocodiling or alligatoring: A drastic type of crazing producing a pattern resembling the hide of a crocodile or alligator.

Cratcring:

The formation of small bowl shaped depressions in thefilm of a confirrg nlaterinl.

80

Curtaining, sagging:

A downward movenlent ol' a paint Tilrn hctwcen the times of' application and setting, resultirig in an uneven coating having a il~ick lower edge. The resulting sag is usually restrictcd to a local arca of' a vertical surlicc and may have the characteristic appcararicc of a draped curtain, llcncc thc synonymous term curfoirring.

Mud cracking: A network of deep cracks that form as the film of a coatirlg material dries, especially when i t has been applied to an absorbent subsfrate. Mud cracking is associated primarily with highly pigmented wafer-borne paints.

i Dry spray:

The production of a rough or slightly bitty film from sprayed coaling malerials where I the pirricles are insufficiently fluid toflow together to form a uniform coal

I Efflorescence:

The uniform pock-marked appearance, in particular of a sprayed film, resembling the peel o i an orange due to the failure of thefilm to flow out to a level surface.

10

20

30

40

NOTE. See also .rprcry n~rrrlle and pock-nwrkinx.

NOI a pninl defecf. It is the development of a crystalline deposit on the surface of brick, cement, etc., due to water containing soluble salts, coming to the surface, and evaporating so that the salts are deposited. In some cases the deposit may be formed on the top or any paint film present, bur usually the paint film is pushed up and broken by the efflorescence under the coat.

Flaking:

Lifting of the coating materials from the substrate in the form of flakes or scales.

Flocculation:

The development of loosely coherent, pigment agglomerates in a coating material.

Grinning through:

The showing through of the substrate due to the inadequate hiding power of the coating marerial.

Holidays:

A defect due to faulty application techniques seen as areas where the film or a coating material is of insufficient thickness or where there is a complete absence of coating malerials on random areas of the substrate.

Lifting:

Soften~ng, swelling or separation from the substrate of a dry coal as the result of the application of a subsequent coat.

Orange peel effect:

The formation of minute holes in the wetfilm of a coatirtg material that I'orni during application and drying due to air or gas bubbles in the wetfilm which burst, giving rise to small craters that fail to coalesce before thefilm has set.

Residual tack: I The degree of stickiness remaining in afilm of a coating malerial which, al~liough set.

does not reach the true tack-free stage.

Ropiness:

Pronounced brush marks that have not flowed out because of the poor levelling properties or the colrting nmterial.

Saponification:

Not specifically a paint defect term. The formation of a soap by the reaction between a fa~ty acid csLcr and an alkali.

NOTE In painting pnctice. .rcrl)ortificcrlrcm refcn to the deco~npsition of the n~c.rlrurrc of a li1111 by alkali and Inolsture In ~ h r sub.~lrule, e.g. new concrete or rendering based on cement, sand nntl IIIIIC Sapon~fied li11rr.v rtl:ly ticcol~te sticky and tliscolollred In very severe cases the filur rnay hc cornple~cly I~qucfied by rer/u~nrlic ctlrorr

Wrinkling, rivelling:

Tlic devcloptnent of wrinkles i n nfilrtl of a catiling malerial during rlr~rn,y, usually due I(> ~Iic t t l t [ ~ i ~ l I'orniation ol..? surf:~cc skin. NOTE Scc ;~lso e.rrrrklrrr~ andfirrrsh

Huane & Il T P O'Nei

COSHH Iiegulations 1994

l o Scope The Control of Substances Hazardous to Health (COSHH) Regulations 1994 (SI No. 3246) define a substancc hazardous to health as:

20

Employers must prevent exposure to substances hazardous to health. or control cxposure when total prevention is not reasonably practicable. Personal protective equipment, e.g masks, are a second choice for control.

a. a substance listed in part 1 of the approved list as dangerous for supply within the meaning of Chemicals (Hazard Information and Packaging) Regulations 1993 and for which an indication of danger specified for the substance in Part V of that list is very toxic, toxic, harmful, corrosive or irritant.

b. one which has a maximum exposure limit (MEL) in Schedule I of COSHH or if the H & S Commission has approved an occuparional exposure standard (OES).

c. a biological agent. d. dust in air - when substantial. e. a substance comparable with the above.

The COSHH regulations are not applicable to the control of lead, asbestos. radioactivity, explosive or flammable properties of materials, high or low temperatures, high pressures, medical treatment or below ground work (mining). Other Regulations deal with these areas.

40

Prior to work commencing, employers must always carry out a risk assessment for all substances hazardous to health to which employees may be exposed.

Responsibilities The exposure of an employee to substances hazardous to health is under the control of the employer. A training organisation is responsible for exposure by trainees.

701 Occupational Exposure Limits (EH40) The G l ~ i c l o n c e Note Eff40, entitled Occupational Exposure Limits, is a docurnen(

60

The occuprrrionrrl exporurr fi!rlir/r,r xylene is UII

occupuIloncrl exl,o.rure srundurd (0E.Y). rherefirc rhc OES is 100 pprn.

Employees have a duty to report any problems in exposure control procedures or any defects found in protective equipment.

Employers must keep records of examinationdmonitoring tests carried out. These are kept for 5 years; 40 years for identifiable employees.

published by the Health and Safety ~xecut ive and updated each year which gives occupational exposure limits for substances hazardous to healtl~.

An organic solvent, which is a substance hazardous to hcalth. has its own occupational cxposure liinil as given in EH40.

Thc toxicity value of a solvent is expressed in pcrrts per million (ppm), e.g. thc occupational exposure limit for xylene is 100 ppm, this means to say that if ' the air contained xylene exceeding 100 ppm the air would be considered to be a significant hazard to hcalth.

There arc I W O types ol'occupational exposure limit:

I . Mnxi l r ru l l l e,vposure l i m i t (MEL): 'is tllc nlaxlmunl cxposurc limit Tor tllal substal~ce set out in Schcdule I in.rclation to the reference period specil-icd (in COSHH) whcn calculated by a ~netliod i~pprovcd by the Health & Saicty Colnmislon.'

2. Occriparionul exposure stundard (OES): 'the standard approved by the Health & Safety Comrnision for that substance in relation to the specified reference ~eriotl when-calculated by a method approved by the Health & S ' a ~ e t ~ ~ornrnision."

When a MEL is specified, exposures must be kept as low as is reasonably practicable, but always below the specified value.

10 k ~ n g term expo.rure 1itnir.r (Ire uveruged over an 8 hour reference period. Shorr fern1 exposure li~nirs ore r u k e ~ ~ over u I5 minute reference period.

An OES should not be exceeded, but, an exposure over the limit is acceptable providing that the reason for exceeding the OES has been identified and measures are taken to reduce the exposure below the OES as soon as is reasonably practicable.

Examples of solvents with their corresponding long term exposure limits (OES's unless otherwise specified) can be seen in the following table:

Solvent Examples with Corresponding OEL's I

Ethers I Ethyl ether 1 Isopropyl ether

Esters

OEL ( p p d

200 1000

Group I Name

Methyl acetate Ethyl acetate Isobutyl acetate

Alcohols Methanol Ethanol

I I Carbon tetrachloride 1 2 1

Ketones

Hydrocarbons (Aromatic)

Hydrocarbons (Aliphatic)

Ch lorinated hydrocarbons

1 "MEL.

kcetone 750 M.E.K. M.I.B.K. 1 200

5 0

Miscellaneous

hMaxirnum short term exposure limit: 450 ppm. LMaximum short term exposure limit: 150 ppm.

Xylene Toluene Benzene

rr-Octane Hexane White spirit

I , I . I-Trichloroethane Trichloroethylene

I

100 50 5

3 00 500 100

35Wh 1 00"

Methyl chloride

Water Nitromethane

released into the atmosphere - 35% to 50% of which came fioln paints. As an exa~nplc of weight volume ratio, e';lch litre O F car paint contains 0.5 kg (1.25 Ib) of VOC's. Each gallon (4.55 litres) of industrial coating car1 contain 4-5 Ih ( 1 8-2.3 kg) of VOC's.

The Europcan Conlrnunily directives are demanding ;I reduction of 30% VOC clnissions by 1990, will1 further reductions [llcrcaftcr. The Unitcd Kingdom El~vironmenlal Prolcction Acl of' 1992 goes evcn Iclrthcr, rccli~iring a reduction of 38%:

5 0

100

Depcndin~ on the conrc.cr (11 [Ire sentence, VOC c . i r ~ ~ nlrtrtr vrllutile O r r l l l ~ c , t t l , , , wlrrri~c orxunic o~nrrnr

0 Hnoanc .lr TI' O'Ncill Isscac 2 2111 U.16

Volatile organic compounds V01:ltile Organic Colnpoilnds (VOC's) are toxic and harlnlul to the environment. I t is estimated that in 1992 in the United Kingdom alone, 1.8 million tons of VOC's were

Ruane & T P O'Neji

of VOC by 1998. COSHH Regulations also require paint manufacturers to screen all raw material used in the manufacture of their product and eliminate, where possible, all materials which may be dangerous to manufacturing operatives and to applicators.

The alternatives to standard paints containing organic solvents are solvent free paints (100% VS), high volume solid paints. i.e. over 65% VS, water borne paints and powder coatings.

Most paint manufacturers have chosen their particular product path, some have opted for acrylics and vinyls, some for new formulations of water borne epoxies and some for 100% VS. Each of the systems have their advantages and disadvantages, e.g. 100% VS urethanes have no VOC's; they are mainly fast curing; highly resistant to chemical attack; chalking and natural erosion is virtually nil but the, activator chemicals are extremely toxic.

High volume solid paints still contain VOC's and therefore in the future their use is likely to be restricted.

Water borne coatings are environmentally friendly and biodegradable, therefore extra costs are not incurred in disposing of containers and sludges etc. but application areas are significantly reduced because of the slow evaporation rate of the solvent water. Water borne epoxies have been in use for some time now, but when used in high humidity environments their successful application and attainment of intended properties is difficult to achieve.

Powder coatings can be applied as thin as 25 pm electrostatically with a utilisation yield of 98%. The disadvantage is that costly heat is required for the reaction. The component needs to be heated to a minimum of 70°C (over 200°C in some cases) to melt the powder in order to form a film and for the reaction to take place. Powders can be formulated to melt at much lower temperatures but this would create manufacturing problems and storage stability problems.

Water borne epoxies are ofien referred to ar new generation or third generation epoxies.

( Health & Safety data sheet

I The information typically present on a health and safety data sheet is as follows:

I . Date of issuc.

2. Product namelreference and manufacturer.

3. Intended usc.

1 4. Health hazards:

a. OEL (8 hours & 15 minutes). b. Respiratory: skin; eye; long term effects.

5. Flammability - fire prevention, fire fighting. a. Flash point. b. LEL and UEL. c. RAQ (to 10% of LEL), e.g. 100 m' of air per litre of paint applied.

1 6. Requirements when handling - barrier creams, masks etc..

sol 7. First aid procedure.

8. Storngc.

9. Spillnpc.

10. Environmental.

I I. Additional i~iform;~tion.

Ruane & P ormill

( Duties of a painting inspector The duties of inspection personnel are essentially those inspection duties which [he client or employer wants them to perform. A significant problem in industry is that different organisations use inspection personnel in different ways, or use inspectors for functions additional to inspection. For some, this has led to a misunderstanding as to the defined role of inspection.

The definition of inspection to BS EN 45020 : 1993 : Standardization and Related Activities - "Evaluation for conformity by measuring, observing, testing or gauging the relevant characrerisfics." ... "Evaluafion for conformity" is defined in the standard as: "Systematic exnminution of the extent to which a product, process or service fulfils specified requirements. "

20

Inspection may be performed for fitness for purpose or quality control purposes, and may be carried out by the contractor, the client or a third party.

The definition of inspection to BS EN 28402 : 1991 : Quality Vocabulary - "Activities such as measuring, examining, te~ting, gauging one or more characteristics of a product or service and comparing these with specified requirements to determine conformity. "

1 Inspection is not supervision and inspection is not a substitute for supervision.

The ugreed rpecificarion(r] f i r rhe contract m y consist clja cornbinution rljone or more of the following:

- ncrtionaUinrernarionrrl .rpecr~icarion(.rJ

- client spcci/icarion(s) - job pecificurion(r)

procedure spccrjicution(s)

It is not the duty of an inspector to deviate From specified requirements; generally speaking, if the specification is inadequate the work will be inadequate. Inspector qualification schemes do not require, or test for, a sufficient depth of corrosion engineering. p a i n t technology or design knowledge which would enable an inspector to pass judgement on the correctness of an application specification. It could be argued that experienced senior inspectors may be in a position to take certain engineering decisions, but i t is dangeroils to generalise on this point.

There was a situation where a client's senior representative became initated because a painting inspector under his control would not allow painting to take place because the relative humidity and dew point temperature were outside the specified requirements. Adverse environmental conditions had persisted over a period of a few days and production was suffering. The client's representative argued that the painting inspector should ha"e allowed painting to continue because it was "common sense to do so".

The inspector had not been given an instruction, either verbally or in writing, to allow this specification deviation. It was being argued that a painting inspector should allow deviations From the agrced specifications at his discretion. Examples like this lead to confusion regarding inspecrors' duties and authority. Inspectors are usually taught never to deviate Srorn tho agrccd spccifications unless given written permission to do so from the client or supervisor.

Accurate reporting is an inlportant duty lor any painting inspector, but what constitutes an accurate report can dilfcr between organisations and projects. Who the inspector actually reports to is also an important consideration.

This is nor to say a palntilig inspector should not perform duties outside the scopc of' inspectiorr, this may t1c acccptablc providing the person is competent to perform thc work and providing I r Iias Ixcn made clear what is required From the outset.

,, It should be made clear to all workers, including inspectors, as to what is expected from them For the activities they are to perform - this is a basic quality assurance requirement.

Ruane & T P OINei/

The following is a list of points which form the basis of typical activities performe painting inspectors:

General: Obtain or gain access to the specification(s).

Learn the specification(s).

Ensure your instruments are in proper working order.

Get to know the plant.

Get to know the personnel.

Check work for conformance to the specification.

Keep the engineerlsupervisor informed at all times especially if there is 1

departure from the specification.

Make written reports at an agreed frequency.

Attend site meetings when required.

At the beginning of the day

Check the environmental conditions.

Check the equipment (preparation, application and inspection equipment 1 conformance to specification).

Check the materials.

Check the previous days work where applicable, e.g. for film contamination a1 DFT if wet films have been left overnight).

Establish with the contractor's senior personnel the day's work programme.

During the day

Check the environmental conditions.

Check the equipment.

Check the usage of materials (when specifically required to do so).

Check each operators work.

On completion of the work a t each stage

Ensure that the work meets the specification by carrying out or witnessing tests.

Check for any application faulls.

At the end of the day

Check the days work.

Check the housekeeping.

Complete reports.

On completion of the job

Ensure as objectively as possible. [ha[ the specified requirements liave beer satisfied..

Write a summary report i f required to do so.

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Ideally, painting inspection personnel should be issued with relevant procedures anc work instructions to enable them to carry out inspection and associated activities i n accordance with the client's or organisation's requirements. The procedures should lcavc the inspectur i n no doubt as to what is lo be donc. Unfortunately, this documentation rarely exists!

/ Typical inspector's duties

I Before work commences

I 2. Ensure [lie contractor's supervisor is aware of your duties and authority.

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I . Determine your duties and responsibilities. Duties may include those which relate to health and safety aspects taking into consideration mandatory requirements. You may also be required to check that rejected paint or used abrasive is disposed of correctly or quarantined.

4. Determine the order of precedence for normative documents if the specification does not make it clear.

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1 5. Learn the specification, procedures. work instructions etc..

3. Ensure you have correct applicable specification(s) and data sheets. Also ensure you at least have access to relevant referenced normative documents.

I 6. Approach the senior inspector or supervisor if you are not sure what is intended of

30 any requirement.

7. Ensure you have copies of any applicable documentation, e.g. correspondence, minutes from meetings, concessions etc..

8. Liaise with the contractor's supervisor to determine whether the contractor's personnel are familiar with the work requirements.

-1 9. When required, confirm that the contractor's operators are properly trained and conversant with the equipment, materials and application techniques being used.

I 10. Agree with the client/supervisor the level of liaison that is required and determine reportinglrecording requirements.

/ Surface preparation

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Check the specification, procedures and/or work instructions to establish: standard against which work is to be measured; methods by which work is to be assessed, e.g. surface comparator; degree of surface cleanliness required; surface profile requirements (where applicable); any special tests to be carried out, e.g. for detecting/measuring degree of surface contamination, sieve analysis of abrasives; requirements regarding equipment and consumables; ambient conditions required; rccording/reporting require~nenls.

I I . Ensure you have test instruments etc. that are required and that they are properly calibrated and in correct working order.

1 2. Check the condition of the substrate before cleaning and make a note of rust I grade, general contours (sharp edges, burrs etc.), spatter or flux residue on welds.

algae or mould growth, zinc salts etc.. Any areas suspected to be defective. e.g. cracked, laminated or mechanically damaged, should immediately be reported to the supervisor or client.

Notc: Do not allow surface laminations. cracks and similar to be dressed without the permission of the supervisorlclicnt.

Ruane & T P OVNei//

3. Ensure ambient conditions allow surface preparation to take place. The following [nay havc to be assessed/measurcd:

a. Air Temperature. b. Steel Temperature. c. Rclative Humidity d. Dew Point. e. Moisture on substrate. f. Potential sources of contamination, i.e. chemicals, salt spray, fumes, dust.

g. Potential changes in the weather to adverse conditions.

4. Identify areas being prepared.

7. Record the results of the inspection. The areas inspected must be identified in the report ensuring that it is clear what has been accepted and what has been rejected. The reasons for any rejections should be clearly identified.

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8. Ensure that all concerned are clear about the reasons for any rejections.

5. Check that the correct materials and equipment are being used, e.g. correct type, correct size, consumables are free from contamination. etc.. Examples:

a. Abrasive type, size and cleanliness. No re-use of expendable material. b. Correct wire brushes. c. Correct needles on needle guns. d. Presence of carbide tips on scrapers. e. Correct chemicals for chemical cleaning.

6. Cany out inspection of prepared surfaces as required by the specification.

9. Where remedial work has been necessary, re-inspect for conformance to the specification.

Paint material

Check the specified requirements.

Check that the paints delivered to the work place correspond to the requirements of the specification and data sheets. The specification may require certain information to be displayed on each paint container.

Check that all paints to be used on a surface are supplied by one paint manufacturer (unless otherwise specified).

Check that the paint is the correct type for the application method being used. i.e. brush grade or spray gradc.

Check the paint storage conditions against manufacturer's recommendations.

Note: Any warranty on the material is likely to depend upon proper handling and storage.

Determine whether the paint is bcing withdrawn from the store in proper rotation. i.e. usually on afirsr in. firs1 our basis.

Ensure paint is not being uscd beyond its shelf life.

Monitor material usagc to detcrniine whether there is sufficient paint in storage for the completion of the job (or part job). (This is not always a responsibility of the inspector).

Check that thc paint is being nlixed and stirred correctly. Any permitted addition of thinners must he rnonitorcd to ensurc correct type and amount. For two pack paints:

check that thc rnatcrials arc rn~xcd strictly in accordance with the paint manufacturer's datashcets, c.g. add P n u B to Part A in the correct ratio; confirm that any induction tinlc is strictly adhered to or time is allowed for gas bubbles to escape ( i f ;~pplicablc); confirm rllnt nlixcd rrlatcrial is not ltsed after its pot lilc.

10. Conduct that all necessary paint sampling procedures and tests; or confirm [ha[ such tests have been carried out prior lo [he commencement of -work. Record

I hatch numbers of painis tested

I Paint application

101 I. Check the specified requirements.

2. Check that the surface to which the paint is being applied is free from contamination, i.e. oillgrease, dust, spent abrasive, corrosion products etc.. Any areas suspected as being defective, e.g. cracked, laminated or mechanically damaged, should immediately be reported to the supervisor or client.

3. Ensure that the ambient conditions allow painting to take place. The following may have to be assessed/measured:

a. Air temperature. b. Steel temperature. c. Relative humidity d. Dew point temperature. e. Moisture on the substrate. f. Potential sources of contamination, i.e. chemicals, salt spray, fumes, dust.

g. Potential changes in the weather to adverse conditions.

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Note: Check that the particular paint being applied does not have any special restrictions on its application.

Note: Do not allow surface laminations, cracks and similar [o be dressed without the permission of the supervisorlclient (not usually the remit of a painting inspector).

I 4. Confirm that paint is not being applied to coated substrates either before or beyond the specified overcoating times for the existing coating.

'01 5. Check that the correct application method is being used.

1 6. [dentify areas being painted.

( 7. Confirm that stripe coats have been applied correctly (if specified).

8. Carry out inspection of painted surfaces as required by specification. For example:

a. Check that each coat of paint is uniformly applied and is free from curtains, sags, runs, holidays or other visible defects.

b. Measure the wet lilm thickness (w.f.1.) immediately after application. c. Measure the dry film thickness (d.f.1.).

Note: If there are significan[ differences between ( I ) the d.S.1. calculated from the w.f.t. and (2) the measured d.f.t., check the material to ensure that only permitted additions of tllinncrs were made to the paint - if possible!

1 9. Ensure that any areas of defective coating are identified for remedial work.

I 0 Ensure that all concerned are clear about the reasons for any rejections.

I I. Re-inspect any remedial work carried our to ensure that i t conforms to the specified requirements.

/ 12. Check tllat the complered work is unilor~ll in colour and finish,

13. Unless the specification statcs otllcrwise, check that the handling of recently coated items is carried ou[ in such a way that the coatings are not damaged.

,, 14. Record the results of the inspcc~ion. The areas inspected must be identified in the report ensuring that i t is clear what Itas bccn accepted and what has been rejected. The reasons for any rejections sllould he clearly identified.

Ruane & T P O'NeiI

2. Ensure that you effectively organise your time so that you are available for inspections when required. Do not give the contractor an excuse to say. "we were waiting for the inspector to carry out inspection".

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1. When required, attend appropriate meetings, such as periodic on-site meetings or those meetings called to provide solutions to a particular problem that has arisen. You may also be in a position where you need to arrange a meeting to resolve problems that have arisen.

4. On completion of the worktcontract, ensure that all records (specifications, procedures, work instruction, permits, concessions, plans, report sheets etc..) are collated and filed in the appropriate location. This is only required when it is your designated responsibility.

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5 . Do not seek confrontation. Try and avoid arguments. Never be condescending. patronising or arrogant. Remember the main duty of an inspector is to inspect against specified requirements and report findings. If the specification is not clear on a particular requirement, seek advice from the supervisor or client. Do not accept or reject work based on your opinion alone. Be objective at all times.

3. Check the work area housekeeping. For example, equipment and consumables should be cared for (correctly handled, stored and maintained) and the site or shop should be tidy (free from empty containers, worn brushes, spent abrasive etc..).

I Reports and records

Progress reports are often required and these may have to be produced on plain paper or on specially designed forms.

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The reporting requirements of quality control associated with painting work and the actual information recorded can differ considerably from job to job. The daily inspccfion report is common to most jobs and is often written out on a Daily Inspection Report Form which has a format designed by the organisation that you are representing, i.e. the inspection agency, contractor or client.

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Thc following list shows the doculnen~ation that may exist on a project involving painting inspection and that which the senior painting inspector is more likely to be responsible for collating and controlling effectively until final completion of the work.

Ideally, the exact reporting and recording requirenlents should be specified in a p c e d u r e or in the job specification itself Always liaise with the supervisor or client verify what is required to be recorded or reported.

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2. Proccdures and related work instructions.

3. Quality plans.

Regardless of specification requirements, the inspector should always nuke a detailed log of work performed, observations, relevant conversations and similar; include applicable times, dates, people involvcd etc.. You may find this information very userul in Suture disputes.

1 5 . Concessions (waiver or variation ordcrs)

6. Daily inspection report forms.

7 . A t l i ~ i l y log (this may be .sln~~r/-nlotrc. docun~cnl or onc in adcltl~on lo a daily lnspcctinn report).

X . Lists of' ~.c~ncdial action

Progress reports.

1 10. Minutes of meetings.

I I I . Correspondence.

12. Calibration certificates.

13. Copies of work permits.

1 14. Site instructions.

15. Mechanical completion certificates (hold-point release forms or inspection request forms).

1 17. Non-conformance reports.

20 16. Audit reports a. Internal. b. External.

I Knowledge required to perform painting inspection

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18. Certificates of conformity.

However, i t is useful to list the subject areas likely to be encountered in industrial painting and to give an idea of the scope and depth of knowledge required in each subject area. This information would provide the core of any training programme to train painting inspectors and the subjects would normally include the following:

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Quality assurance basics. Inspection philosophy. Types of normative documents and their interpretation. Corrosion basics. Surface preparation. Paint technology (basic knowledge). Coating systems. We! painvpaint film testing. Inlluence of environmental conditions - %RH, dew point etc.. Paint application methods. Coating faults. Health and Safety. Environlnental considerations - waste disposal. Reporting.

The knowledge required for a painting inspector to c a n y out his duties obviously depends on what his duties are, which differ from job to job according to the surface preparation methods, paint systems used and the client's specific requirements.

For some work, knowledge will be required of other subjects not identified above, c.g. insulation, firc proofing, anti-fouling, cathodic protection.

Whether a painting inspeclor has the knowled,oe required to give enough confidence that helshe can adequately perform the duties specified should be determined by the employer and usually the clicnt. It is thought that the most appropriate or simplest method of doing this is to specify the use ol'ccrtified inspectors, e.g. ICorr. NACE or B.G.A.S. But /low Inany people specifying this requirement actually know what is contained within the syllabus and whether the inspectors are likely to have the knowledge requircd for the work to be pcrl'ormcd*! It [nay be necessary to give inspectors additional training outside the scope of the cxalnination syllabuses for some work.

Unfortunately, w e are not in an ideal *or-ltl. 111 practice, the specification(s) and instructions issued d o not always prepare inspectors for the actual situations which arise - despite tllc cfl'orts of QA and planning personnel. I t is not an unusual situation to find

that the painting inspector on location is the person in the best position to pass judgement on a painting related problem which is really outside the scope of his knowledge and he may be in a situation where a decision has to be taken immediately, i.e. he may not be able to consult others who have the knowledge. But effort is still required to try and prevent situations like this arising.

Typical contractor malpractices Typical contractor malpractices which the inspector should be aware of are as follows:

I. Use of unskilled operators. This may relate to surface preparation, application of paint or safety considerations, e.g. unsafe scaffolding. Note: The painting inspector cannot normally report an unskilled operator as something which does not conform to specification.

2. Use of unsuitable equipment, which may be worn brushes, poorly maintained and leaking compressors, damaged ladders, contaminated equipment from previous contract etc..

3. Painting or preparing surfaces during inclement weather conditions such as rain, snow, fog. mist etc..

4. Hand mixing paint which should be mechanically mixed.

4 0 1 5. Painting before inspection of substrate preparation or previous coat.

6. Applying two paint coats or more to the same area in one day assuming specification does not allow this.

Using die.~el in rlze puirrr ( ( IS u ~hinner rrr l~lusricirer) h0.r been done tm m n y r>c,ccurions! This will prevent proper drying.

1 12. Rc-using expendable abrasives.

1 I). [nsulficient blasting or painting in difficull access areas such as under pipes.

7. Missing out a coat.

8. Use of wrong solvent or an excessive amount of solvent.

9. Use of incorrect paint type or mixing different manufacturers' products.

10. Storing paint incorrectly, e.g. where the specification requires paint to be stored in a temperature controlled environment.

I I . Paint used outside the expiry date, suspected by condition of can, excess binder on top of freshly opened can, pigment settlement. Check the date by way of the manufacturer's coding; inform engineer.

7 0

14. Cleaning surfaces with contaminated cotton waste or rags or using materials for cleaning which are not permitted.

15. Applying a thickness of paint which is less than the specified minimum.

A paint data sheet is produced by the paint manufacturer and is an information sheet relating to a specific paint and its application. Health and safety information applicable to the paint may form part of the data sheet or may be supplied separately.

Paint data sheets must be obtained by the painting inspector either from the paint contractor or client, or possibly direct from the source, i.e. paint manufacturerIsuppIier depending on the particular job. All data sheets contain similar information as shown on the following examples: t

I CHLORINATED RUBBER FINISH (HIGH BUILD)

201 / Description.

This coating is based on a halogenated hydrocarbon resin modified with an insaponifiable plasticiser. The opacifying pigment used is rutile titanium dioxide. This material has been specially formulated giving a long coating life at a minimum dry film thickness of 100 p.

I Characteristics.

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50

60

'0

This material is so designed that ultimate failure is due to slow natural erosion leaving an ideal substrate for recoating. Thus, future maintenance is confined to the application of a single coat at five year intervals without any costIy surface preparation. This paint has excellent resistance to distilled. tap or sea water and has shown excellent resistance to salt spray (6000+ hours duration), humidity cabinet (2000+ hours duration) and can be used at temperatures up to 80°C.

Consistency and method of application

Weight p e r 5 litres

Volume solids

Theoretical spreading rate

Practical spreading rate

Wet film thickness range

Dry film thickness range

Application instructions

Flash point

Surface d r y Hard d ry Overcoating

Cleaning solvent (or thinners)

Colours

Thixotropic. Brushing

6.75-6.32 kiIograms

42%

22m2 per 5 litre @ 100 prn d.f.t.

17m2 per 5 litre @ 100 prn d.f.t.

180-300 pm

75- 125 pm

Stir well before use. Apply liberally, as supplied, by brush, in well ventilated conditions. Monitor w.f.t.

42°C

2 hours 8 hours 16 hours

Ref. 123

White and pastel shades to any agreed range

Ruane & // T P O'Nei

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I

L

L

b

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I

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50

60

70

80

90

0

MICACEOUS IRON OXIDE PAINT

Description.

The leafing characteristics of micaceous Iron oxide, combined with the modified phenolic resin and trcated oils, ensure a film with good protective and anti-corrosive properties.

Characteristics.

This paint is designed to provide a tinish w~lh maximum durability and weather resistance. Excellent for the protection of exposed steel.

- P I

1 u , i

Hunnr d r 1 ' 0 h ~ # l l I \ r u c I llldlllN7 P14-2

Consistency and method of application

Weight per 5 litres

Volume solids

Theoretical spreading rate

Practical spreading rate

Wet film thickness range

Dry film thickness range

Application instructions

Flash point

Surface dry Hard dry Overcoating

Cleaning solvent (or thinners)

Colours

Normal. Brushing

7.75-7.95 kilograms

47%

50m2 per 5 lltre @ 50 pm d.f.t.

37m2 per 5 litre @ 50 pm d.f.t.

80- 110 pm

38-50 pm

Stir well before use. Apply as supplied by brush in well ventilated conditions. Monitor wet film thickness.

37°C

3-5 hours 6 hours

16 hours

Ref. 234

Steel Grey Ref IAB Silver Grey Ref 2AB Green Ref 3AB Black Ref 4AB Blue Ref 5AB L~ght Grey Ref 6AB

ZINC PHOSPHATE EPOXY BLAST PRIMER I

Film does not reach maximum resistance until approximately 7-10 days after application at 18°C. Do not leave longer than 48 hours between coats.

10

20

30

40

50

Description. Cold cure epoxy zinc phosphate primer (two pack). Base Ref 2AB 123: Curing agent

Consistency and method of application

Weight per 5 litres

Volume solids

Theoretical spreading rate

Practical spreading rate

Wet film thickness range

Dry film thickness range

Application instructions

Flash point

Surface dry Hard dry Overcoa ting

Cleaning solvent (or thinners)

Pot life

Ref. 4AB 234

Normal. Brushing

Base - 7.6 kilograms Curing agent - 4.8 kilograms

5 1 % blended

83m2 per 5 litre @ 30 pm d.f.t.

62m2 per 5 litre @ 30 pm d,f.t.

50-60 pm

25-30 pm

Before using, thoroughly mix 3 parts by volume base with 1 part curing agent. Apply by brush, in well ventilated area. Monitor wet film thickness.

22-32°C Flammable

30 minutes 2 hours 2 hours

Ref. 456

24 hours @ 16°C

Ruane & T P OINed

Aim of quality assurance The aim of quality assurance is to improve quality whilst keeping costs to an acceptable level.

The emphasis is on prevention rather than detection and cure.

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I Benefits of adopting quality assurance

The objective of a system used to implement quality assurance, i.e. a qualify system, is to prevent the occurrence of problems which result in remedial action. If problems do occur the objective is to determine and rectify the root cause(s), thereby reducing faults and wastage in the future. This will in turn, improve quality and reduce costs.

1 A properly implemented and managed quality system should:

1 a. help to ensure that the company focuses on market needs and requirements. b. make the company more competitive in the market place due to an increased

customer confidence in the company's output, i.e. a product or service that a customer wants - this includes timing.

c. lead to a reduction of costs due to a reduced number of faults and wastage. d. give a measure of performance which will enable any areas for improvement to

be identified. e. induce a more organized way of thinking which makes management more

organized and effective. f. provide motivation; motivated employees provide a better working

environment in addition to the product or service output benefits.

'01 What is quality assurance? The definition for qualify assurance given in IS0 8402 : 1986 (BS 4778 : Part 1) entitled Qualify vocabulary:

I 'All those planned or systematic actions necessary to provide adequate confidence that a product or service will satisfy given requirements for quality.'

I Quality assurance provides the objective evidence needed to give maximum confidence for quality.

60 The quality o'f a product or service is attained only by working in a controlled manner, following formalised procedures which are designed to eliminate the occurrence of problems.

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Contract documents or purchasing specifications should clearly define a company's requirements for a product or service. The quality of the product or service is deemed to have been achieved when the exacl requirements have been met completely and consistently - assuming correct specification!

Quality assurance may be considered as a management tool when used within an organization. A supplier that implements and maintains a system for assuring quality. is providing maximum confidence to a purchaser, or potential purchaser, that the supplied product or service attains, or is going to attain, its fitness for purpose.

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Different people have different concepts for what is meant by a qualify product or service, therefore it is very important to be aware of the customers' requirements andlor expectations.

Ruane & T P O'Nei//

Scope of quality assurance - I-- 10

Quality assurance should encompass all parts of an organization and all phases of an activity, i.e. planning, design, production, maintenance, administrative etc. in order to give a purchaser, or potential purchaser, maximum confidence that the client's expectations for quality have been met. Collaboration with suppliers and purchasers should also be part of an organization's quality system.

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QA standards BS EN IS0 9000 series - Quality systenrr.

B S 4778 - Quality vocabul~ry. [ E N 28402; IS0 84021

BS EN 3001 1 - Guidelines for auditing quality systems.

QA, QC and inspection compared Quality assurance is not inspection. Inspection is one of the important elements within a system for quality assurance. Inspection requires continuing evaluation in the same way as the other elements, e.g. planning, designlspecifications, production etc ... Inspection is defined in BS 4778 : Part 1 as: 'activities such as measuring, examining, testing, gauging one or more characteristics of a product or service and comparing these with specified requiremenb to determine conformity .'

Inspection is also defined in EN 45020 : 1993 : Glossary of t e r m for standardization and related activities: 'Evaluation for conformity by measuring, observing, testing or gauging the relevant characteristics.' Evaluation for conformiry is defined in the same standard as: 'Systematic examination of the extent to which a product, process or service fulfils specified requirements.'

Quality control is defined in BS 4778 : Part 1 as: 'the operational techniques and activities that are used to fulfil requirements for quality.' This definition can be vague. so modifying the term to be more specific is advantageous, e.g. manufacturing quality control.

Quality control is involved with the monitoring of a process and eliminating the causes of any deficient output of a process, or any phase during a contract, which has an effect on quality. The information obtained from inspection, as defined above, is used for quality control.

Quality control deals with the actual measurement of quality performance which is compared against what is required and action is taken on the difference. Quality control is asking the question, "is the worwaction being performed correctly"?

Quality control does not reach all elements which affect quality, e.g. quality control will rarely do anything to correct problems relating to management, traceability, training and staff motivation.

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Quality assurance applies to all areas which have an affect on quality, and asks the question, "has the worklaction been performed correctly"? This question can only be asked after information has been obtained from qualily concrol and all other departmen~slareas which affect quality.

Normative document: Document that provides rules, guidelines or characteristics for activities or their results. Note: The term nornzative document is a generic term that covers such docutnents as standards, technical specifications, codes of practice and regulations. [IS0 Guide 2 & EN450201

Standard: Document, established by consensus and approved by a recognized body, that provides, for conimon and repeated use, rules, guidelines or characteristics for activities or their results, aimed at the achievement of the optimum degree of order in a given context. [IS0 Guide 2 & EN 450201

Code of practice: Document that recommends practices or procedures for the design, manufacture, installation, maintenance or utilization of equipment, structures or products. Note: A code of practice may be a standard a part of a standard or independent of a standard. [IS0 Guide 2 & EN 450201

Specification: The document that prescribes the requirements with which the product or service has to conform. Note: A specification should refer to or include drawings, patterns or other relevant documents and should also indicate the means and the criteria whereby conformity can be checked. [BS 4778 : Part I]

Technical specification: Document that prescribes technical requirenzents to be fulfilled by a product, process or service. Note: A technical spec~$cation should indicate, wherever appropriate, the procedure(s) by means of which i t may be determined whether the requirements given are fulfilled. A technical specification may be a starzdurd a part of a standard or independent of a standard. [ IS0 Guide 2 & EN 450201

Regulation: Document providing binding legislative rules, that is adopted by an authority. Note: An authority is a body that has legal powers and rights. [IS0 Guide 2 & EN 450201

Procedure (1): Specified way to perform an activity. [IS0 8402 & IS0 10005]

Procedure (2): A written description of all essential parameters and precautions to be observed when applying inspection or a test method to a specific item or quantity of items, following an established standard, code or specification. [ICORR REQ DOC]

Instruction: Provision that conveys an action to be performed. [IS0 Guide 2 & EN 450201

Written instruction: A detailed writtcn descriplion of the inspection(s) or test(s) to bc performed. [ICORR REQ DOC]